Seat

ABSTRACT

A seat comprising a seat frame, and a cushion material supported by the seat frame and having a three-dimensional knitted fabric which is formed by joining, with connecting threads, a pair of ground knit fabrics which are disposed so as to be separated from one another, wherein the cushion material comprising a first region whose elastic compliance when a reaction force is applied to an extending side of the cushion material when an occupant is seated on the seat is substantially equivalent to an elastic compliance of a portion of the occupant&#39;s body pressing the cushion material and a second region whose elastic compliance is larger than that of the first region. Accordingly, a thin and light seat can be provided, load concentration on the occupant&#39;s tuber ishiadicum bottom portion when seated for a long period of time can be mitigated, and vibration-transmitting characteristics can be improved.

TECHNICAL FIELD

[0001] The present invention relates to a seat using a three-dimensionalknitted fabric as a cushion material, and more particularly, to avariety of seats such as a vehicle seat for an automobile or train, anoffice chair, a furniture chair and the like.

BACKGROUND ART

[0002] Lately, a vehicle seat using a three dimensionally structured netmaterial (three-dimensional knitted fabric) which is of a thin-type, butable to exhibit a high cushioning performance, and which has a largenumber of cylinders and is accordingly able to exhibit excellent airpermeability, has been known. The three-dimensional knitted fabric has atruss structure (three-dimensional structure) which does not easilyelastically wear out. The truss structure is formed by using a largenumber of connecting threads to join a pair of ground knit fabrics whichare disposed so as to be separated from one another. Thethree-dimensional knitted fabric has excellent air permeability, bodypressure distribution performance, and impact absorbing performance, andin spite of being of a thin type, can impart characteristics similar tothose obtained by a high elastic polyurethane foam generally used as acushion material.

[0003] However, when a cushion material having high stiffness is usedfor a vehicle seat or the like, a load from a human body is generallyconcentrated on a muscle portion in the vicinity of a tuber ischiadicum.This creates an uncomfortable sensation, and even causes numbness whenan occupant is seated on a vehicle seat for a long period of time.

[0004] On the other hand, it is known that ranges of vibration whichlargely influence riding comfort are around 5 Hz at which range askeleton of an occupant (a human body) swings vertically and at 2 Hz orless at which range a human body swings in a forward-backward(longitudinal) direction. Therefore, it is considered that an idealcushion material should have characteristics whose tolerable vibrationpeak is outside the aforementioned vibration ranges, and in addition,whose vibration-transmitting ratio is relatively low, within a range of6 to 8 Hz, and accordingly, has resonance with the internal organs of anoccupant.

[0005] In view of the aforementioned facts, an object of the presentinvention is to provide a seat using a three-dimensional knitted fabricof a thin and light type and having superior characteristics as acushion material as described above, in which riding comfort can beimproved by alleviating concentration of a load on a tuber ishiadicum ofan occupant, reducing occurrences of numbness when an occupant is seatedfor a long period of time, and compared with the past, alleviatingvibration-transmitting characteristics caused by the impact of vibrationon a human body (seated occupant).

DISCLOSURE OF THE INVENTION

[0006] In order to solve the aforementioned problems, the followingaspects have attracted the attention of the present inventors:

[0007] First, the present inventors reached a conclusion thatconcentration of a load on a tuber ischiadicum bottom of an occupantcauses numbness to occur. This is because, if a cushion material for aseat has high stiffness, the amount of deformation of a muscle portion(including skin) of an occupant pressing the cushion material is greaterthan that of the cushion material. Further, a muscle portion of a humanbody and the cushion material make contact with each other throughclothes and the like of an occupant. However, since the clothes can beignored, hereinafter, in some cases, the term “contacting’ is usedinstead of the term of ‘pressing’.

[0008] In other words, as shown in FIG. 4, when a load (weight) W actson the cushion material, in consideration of a serial connection betweena spring constant k1 of the cushion material and an equivalent springconstant k2 of a muscle portion of the buttocks of a human body, flexureof the cushion material x1 is represented by x1=W/k1, and flexure ofbuttocks x2 is represented by x2=W/k2. For this reason, when k1>k2,flexure of buttocks x2 becomes greater, concentration of a load on atuber ishiadicum bottom portion of a human body and numbness as a resultof concentration of load tend to occur.

[0009] Accordingly, the smaller the spring constant of the cushionmaterial k1 in relation to that of a muscle portion of the buttocks k2,the greater the flexure of the cushion material x1. Therefore, by usinga cushion material which includes a region having a spring constantsubstantially equivalent to or smaller than that of a portion of anoccupant's body pressing (or contacting) the cushion material,concentration of load on a tuber ischiadicum bottom of a human body andoccurrences of numbness as a result of the concentration of load can bereduced. Further, by forming such a region on the cushion material, whena muscle portion of a human body is considered as a material forstructuring a vibration system, a muscle portion behaves as a vibrationmodel at 2 degrees of freedom when having a dynamic vibration absorbingeffect, and it is considered that vibration-transmitting characteristicscan also thereby be improved. In this context, ‘dynamic vibrationabsorbing effect’ means that a pair of thighs of an occupant behaves asa dynamic vibration absorber, and dynamically damps vibration applied toan object which has been mainly formed by a fuselage of an occupant.

[0010] On the other hand, “spring constant” is determined by a relativerelationship between a load and a flexure amount. However, in order toevaluate a very small region (per unit area) of a seat portion which theperiphery of a tuber ishiadicum of an occupant contacts by consideringthat a state in which an occupant is seated on a seat is an equilibriumpoint, it is effective to use as an index an elastic compliance in whichpressure fluctuation is a variable input, displacement is an outputvalue, and a load is converted into a pressure value, i.e., an “elasticcompliance” which is calculated by “flexure amount/pressure value”.Accordingly, providing a cushion material with a region whose springconstant is substantially equivalent to or smaller than that of a humanbody portion contacting (pressing) against the cushion material can beconsidered an alternative to setting a cushion material in a structurehaving a region whose elastic compliance is substantially equivalent toor greater than that of a human body portion contacting the cushionmaterial.

[0011]FIG. 22 shows a flexure characteristic of a muscle portion inrelation to a pressure of a pressurizing plate, a flexure characteristicwhich is measured at a region from the ishium to the vicinities of thethighs of an occupant by using a pressurizing plate having a diameter of98 mm. In accordance with this flexure characteristic, it can be notedthat change of characteristic on the buttocks and thighs are small.Further, inclination of this characteristic (flexure amount/pressurevalue) represents a so-called elastic compliance. A detailed descriptionof elastic compliance will be made later.

[0012] A description of a pressurizing plate having a diameter of 98 mm(hereinafter, a 98 mm-diameter pressurizing plate) will be made next.First, an assumption is made that a mass of a fuselage (trunk portion)of a human body is concentrated on a seat portion which the periphery ofa tuber ishiadicum of an occupant contacts. It is known that a distancebetween two tuber ishiadica for a male adult is 100 mm to 115 mm, andfor a female adult, 110 mm to 130 mm.

[0013] When data for body pressure distribution is evaluated, it isconsidered that a partial stiffness of a cushion material is measured byusing a pressurizing plate whose diameter is 100 mm or less. It is alsoassumed that 80% of a weight of an occupant is concentrated on thevicinity of a tuber ishiadicum, and when an occupant weighs 60 kg, apressurizing plate whose diameter is 200 mm can support 45 kg out of 60kg. When this value is converted into a pressure value, it becomes 143g/cm². In this case, two 98 mm-diameter pressurizing plates can supporta load of 21.57 kg. This value is within a pressure range which the 98mm-diameter pressurizing plate can output, when it is assumed that amaximum pressure value of a seat, which provides an occupant with asense of comfortable riding comfort, is 180 to 200 g/cm². As shown inFIG. 36, this value is approximate to a load mean value which isobtained by integrating a pressure value per unit area, which isexperimentally determined by using q body pressure distribution meter,with a dimension of a 98 mm-diameter.

[0014] In considering 120 kg weight, one 98-diameter pressurizing platecorresponds to a load of 21.57 kg. Accordingly, partial stiffness wasmeasured under the same conditions as those of the 98 mm-pressurizingplate (maximum load: 20 kg). Further, by means of an experiment, it wasconfirmed that a range of a pressure of 80 g/cm² or more, which isconsidered as a reference value on the basis of a capillary pressurevalue, can be concentrated on a pressure range of the 98 mm-diameterpressurizing plate. Further, it was verified that a slender seatedoccupant imparts a pressure value higher than that of a fatter seatedoccupant. Accordingly, when the flexure characteristics of a muscleportion and the like are examined, use of the 98 mm-diameterpressurizing plate is reasonable.

[0015] When the seat portion is formed by polyurethane foam, the seatportion is formed such that an occupant feels sensation of softness at atuber ishiadicum bottom portion, and increasingly hardness toward afront edge portion of the seat portion. However, there is a possibilitythat a front edge portion of the seat portion compresses the rear sidesof the thighs of an occupant thereby causing compression of nerves andimpeding blood flow. Accordingly, it is desirable that the elasticcompliance of a dimension of the seat portion which the thighs of anoccupant contacts (which substantially corresponds to a dimension of the98 mm-diameter pressurizing plate) be greater than that of acorresponding dimension of the seat portion which the vicinity of atuber ishiadicum bottom portion of an occupant contacts. In terms of aspring constant, it is desirable that a spring constant of a front edgeportion of the seat portion be smaller than that of the seat portionwhich the vicinity of a tuber ishiadicum bottom portion of an occupantcontacts, and it is also desirable that it impart a characteristic of asmall reaction force. In particular, when the cushion material is usedfor a vehicle seat, in order to facilitate a smooth pedal operation, itis desirable that the required spring characteristic at a front edgeportion of a seat portion not be excessively large.

[0016] The elastic compliance of the seat portion which a tuberishiadicum bottom portion of an occupant contacts is made to besubstantially equivalent to that of a human body portion contacting theseat portion, and the elastic compliance of a front edge portion of aseat portion is made to be greater than that of the seat portion which atuber ishiadicum bottom portion of an occupant contacts. Accordingly,although a fluctuation characteristic is non-linear, hysteresis loss islarge. Consequently, setting of load occurs, and a reaction forceapplied to a human body can be minimized. As described above,occurrences of numbness in a tuber ishiadicum bottom portion can beprevented and attempts can be made to prevent the impeding of blood flowinto the thighs of an occupant.

[0017] On the other hand, the seat portion which a pelvis front portionof an occupant contacts, which is located about 100 mm forward of theseat portion which a tuber ishiadicum bottom portion of an occupantcontacts, has an elastic compliance smaller than that of a human body(seated occupant) contacting the seat portion. Meanwhile, a linearcharacteristic of the seat portion which a pelvis front portion of anoccupant contacts is more pronounced than that of the seat portion whicha tuber ishiadicum bottom portion of an occupant contacts. Therefore, aregion that functions as a dam can be formed at the seat portion whichthe vicinity of a pelvis front portion of an occupant contacts.Accordingly, an ishium portion of a human body can sink into arelatively large amount, rotation of the ishium can be prevented, andstability of seating posture can be improved. Further, a spring system,which imparts a restoring force against an input force, is intensivelyfocused on a tuber ishiadicum bottom portion, which is a gravity centerof a vertical load when an occupant is seated on the seat. Consequently,efficiency of the restoring force is improved, relative displacement ismade greater by a small frequency band, and reduction of vibration bymeans of anti-phase is made possible.

[0018] The above descriptions are summarized as shown in table 1: TABLE1 pelvis front tuber portion ishiadicum (100 mm in front edge bottomportion front) portion elastic equivalent to smaller than larger thancompliance human body human body human body characteristic non-linearhigher linear non-linear than that of seat portion beneath tuberishiadicum bottom portion spring constant equivalent to larger than thatsmaller than human body of human body that of human body

[0019] Moreover, it becomes important to determine a spring constant ofa muscle portion k and a damping coefficient c in relation to vibrationfrequency in order to set characteristics of the cushion material. Tothis end, simple vibration test were conducted on the buttocks of fourmale adults to examine frequency characteristics of the spring constantk and the damping coefficient c.

[0020] As shown in FIG. 31, an occupant was seated on a seat portionwhich is structured by stretching a cloth spring across a frame of asize: 370 mm×520 mm×320 mm. Vibration was applied to the seat portion byvarying a sine waveform frequency at 1 Hz of from 2 Hz to 10 Hz. Basedon flexure of a tuber ishiadicum bottom portion measured from the rearside of the cloth spring, on an output from a small acceleration sensormounted on the seat portion which a tuber ishiadicum bottom portionscontacts, and on a mass equivalent to 80% of a weight of an occupant asshown in FIG. 32, a vibration model at 1 degree of freedom wassimulated, whereby the spring constant k and the damping coefficient cwere determined by using a state of mass obtained from the experiment.Frequency characteristics of the spring constant k and the dampingcoefficient c of a JM85 (Japanese male/weight 85 kg) are shown in FIGS.30A and 30B.

[0021] Hardness of buttocks was measured from the rear side of the clothspring by a Shore A hardness meter. Since the measured hardness ofbuttocks and the hardness of buttocks during seating posture wereequivalent to one another, the spring constant of the cloth spring wasinsignificant in comparison with that of a muscle portion. Accordingly,the frequency characteristics which are shown in FIGS. 30A and 30B canbe regarded as equivalent to those of the spring constant k and thedamping coefficient c of buttocks.

[0022] As shown in FIG. 30A, the spring constant k decreases in a rangefrom 3 Hz to 6 Hz, turned negative near 6 Hz, and thereafter, reached amaximum near 9 Hz. On the other hand, as shown in FIG. 30B,characteristics of the damping coefficient c increases at around 6 Hzand 7 Hz where the spring constant k turned negative. As shown in thefrequency characteristics of flexure of a muscle portion of the buttocksin FIG. 33, it can be deduced that the spring constant k turns negativenear 6 Hz because there are two vertical resonances near 4 Hz and 9 Hz,and there is anti-resonance near 6 Hz. It can be inferred that the tworesonances were caused respectively in the vicinity of 4 Hz on accountof a mass of an upper body and in the vicinity of 9 Hz ion account of amass of a waist portion of a human body. However, these resonancefrequencies are shown as an example of a JM85, and in the case of alight seated occupant, respective resonance frequencies become higher.

[0023] Thus, it has become apparent that, among the characteristics of amuscle portion of the buttocks at below 10 Hz, the spring constant k andthe damping coefficient c are determined in accordance with vibrationfrequencies in a vibration system with 2 degrees of freedom in theseating posture of a human body. Namely, the spring constant of a muscleportion of a tuber ishiadicum bottom portion, on which a greater part ofa cushioning load is concentrated, becomes almost zero in a range of 4to 6 Hz, and it is accordingly important to set the spring constant soas not to cause a muscle portion to collapse at the periphery of a tuberishiadicum contacting the cushion material. Thus, in order to minimizethe spring constant of the cushion material which the periphery of atuber ishiadicum contacts (for example, a dimension of 30 mm-diameter),and to disperse the load into the periphery of a tuber ishiadicum (forexample, a contacting dimension of 98 mm-diameter), it is necessary toset such a spring constant that can change a surface stiffness at theperiphery of a tuber ishiadicum and the nearby region.

[0024] The present invention has been achieved in the light of theabove-described information, and is a seat comprising a seat frame and acushion material having a three-dimensional knitted fabric which isformed by joining with connecting threads, a pair of ground knit fabricswhich are disposed so as to be separated from one another, and whichmaterial is supported by the seat frame, in which the cushion materialcomprises a first region whose elastic compliance when a reaction forceis applied to an extending side of the cushion material when an occupantis seated on the seat is substantially equivalent to that of a humanbody portion pressing the cushion material, and a second region whoseelastic compliance is larger than that of the first region.

[0025] When a load applied to a contracting side of the cushion materialwhen an occupant is seated on the seat, and a reaction force which isapplied to an extending side of the cushion material in response to theload which has been applied to the contracting side of the cushionmaterial are in equilibrium, an elastic compliance of the second regionwhen a very small reaction force is applied to an extending side of thecushion material is greater than that of a human body portion pressingthe cushion material.

[0026] A road surface vibration while a vehicle is traveling is largelyaffected by a load fluctuation characteristic when a weight of anoccupant and a reaction force applied to the cushion material are inequilibrium. In the present invention, when a very small reaction forceis applied to the extending side of the cushion material, an elasticcompliance of the second region is larger than that of a human body (amuscle portion) pressing the cushion material. Accordingly, flexurevariation in relation to the cushion material becomes greater, andaccordingly, flexure variation in relation to a muscle portion becomesless. Consequently, vibration stimulus transmitted to a human body canbe reduced and riding comfort can be improved.

[0027] In the present invention, in order to examine an elasticcompliance of the cushion material during the aforementioned equilibriumstate, a load was calculated in accordance with an average pressure of aregion, which is mainly at a tuber ishiadicum bottom portion having a 98mm-diameter. Then, by using a 98 mm-pressurizing plate which has a massof about 67N equivalent to the obtained load value, vibration having asine waveform with a constant frequency was applied to 150 mm and 250 mmpositions from the rear end of the cushion material. Accordingly, on thebasis of pressure of the pressurizing plate and flexure of the cushionmaterial, elastic compliance in the aforementioned equilibrium state wasexamined.

[0028] A pressure of the pressurizing plate was determined such that aninertia force could be calculated by using an output from anacceleration sensor mounted on the pressurizing plate and a mass, andthe inertia force thus calculated was divided by a dimension of thepressurizing plate. Further, flexure of the cushion material wasdetermined such that a relative displacement between the pressurizingplate and a vibration-applying base was measured by using a laserdisplacement meter. FIG. 34 shows an example of results from anexperimental simulation of the equilibrium state at the points of 150 mm(the periphery of a tuber ishiadicum) and 250 mm, respectively from therear end of a seat surface of the cushion material. FIG. 34 shows agraph in which a Lissajous's waveform, formed by a pressure value of thepressurizing plate and flexure of the cushion material, and a staticmuscle characteristic of FIG. 22 overlap one another.

[0029]FIG. 35A shows a graph illustrating a characteristic at 3 Hz byenlargement of portion A of FIG. 34, and FIG. 35B shows a graphillustrating a characteristic at 4 Hz.

[0030] As is apparent from FIG. 34, gradients of the Lissajous'swaveforms, i.e., elastic compliances at the 150 mm and 250 mm positionshave substantially the same value, that is, about 900 mm³/N. The elasticcompliance is the same as that of a static elastic compliance of amuscle portion. The elastic compliance has substantially the sametendency for each frequency. Further, a value when the elasticcompliance is converted into an average spring constant k of the 98mm-pressurizing plate is 8.3 kN/m. It is noted that this value isrelatively small except values near 6 Hz which are anti-resonance andwhich are shown in FIG. 30A.

[0031] As a result, when a load applied to a contracting side of thecushion material when an occupant is seated on the seat, and a reactionforce applied to an extending side of the cushion material in responseto the load which has been applied to the contracting side of thecushion material are in equilibrium, an elastic compliance of the secondregion when a very small reaction force is applied to an extending sideof the cushion material is greater than that of a muscle portion of thebuttocks (the spring constant decreases sufficiently). Accordingly, thecushion material can absorb a greater part of vibration energytransmitted to a muscle portion of the buttocks while a vehicle istraveling. Consequently, vibration stimulus to a human body ismitigated, and riding comfort is improved.

[0032] The first region and the second region are laminated to oneanother such that the second region is positioned on a top layer portionof a seat portion, or alternatively, the first region and the secondregion can be disposed such that the second region is positioned at afront edge side of a seat portion and the first region is positioned ata predetermined region including a tuber ishiadicum bottom portion (theperiphery of a tuber ishiadicum bottom portion) of an occupant. Bylaminating the first region and the second region to one another, asdescribed above, vibration is transmitted to a human body via the regionwhose elastic compliance is greater than that of a muscle portion of ahuman body. Accordingly, vibration stimulus transmitted to a human bodycan be mitigated, and riding comfort can be improved. Further, since thesecond region is positioned at a front edge side of a seating portion,it is possible to prevent numbness of a muscle portion near a tuberishiadicum bottom portion and the impeding of blood flow into thethighs.

[0033] The first region has a region whose elastic compliance is lessthan that of a human body at the lower portion thereof. Accordingly, thefirst region can exhibit elastic compliance substantially equivalent tothat of a human body.

[0034] The present invention is a seat comprising a seat frame, and acushion material including a three-dimensional knitted fabric which isformed by joining with connecting threads, a pair of ground knit fabricsdisposed so as to be separated from one another and a three-dimensionalknitted fabric which is supported by the seat frame. The cushionmaterial comprises a first region whose elastic compliance when areaction force is applied to an extending side of the cushion materialwhen an occupant is seated on the seat is substantially equivalent tothat of a portion of the occupant's body pressing the cushion materialand which is positioned at a predetermined region including a seatportion which a tuber ishiadicum bottom portion of an occupant contacts,a second region whose elastic compliance is greater than that of thefirst region and which is positioned in the vicinity of a front edgeportion of the seat portion, and a third region whose elastic complianceis less than that of the first region and which is positioned at a seatportion which the vicinity of a pelvis front portion of an occupantcontacts.

[0035] Further, in the present invention, the cushion material isstructured such that the three-dimensional knitted fabric is stretchedacross the seat frame, and a portion of the stretched three-dimensionalknitted fabric is mounted on an elastic member which is smaller than thethree-dimensional knitted fabric and whose elastic compliancecharacteristic is substantially linear, and the cushion materialcomprises a first region having the elastic member beneath thethree-dimensional knitted fabric and a second region which does not havean elastic member beneath the three-dimensional knitted fabric. In thiscase, the second region is positioned at a front edge side of the seatportion, and the first region is positioned at a predetermined regionincluding a seat portion which a tuber ishiadicum bottom portion of anoccupant contacts, whereby it is possible to prevent numbness on a tuberishiadicum bottom portion and the impeding of blood flow into the thighsto an occupant.

[0036] The elastic member is provided at a region which has apredetermined region including a seat portion which a tuber ishiadicumbottom portion (the vicinity of a tuber ishiadicum bottom portion) of anoccupant contacts, and which excludes the vicinity of a front edgeportion of the seat portion and a rearward-direction portion from thepredetermined region. In other words, the elastic member can be providedat points between 100 mm and 300 mm from the rear end portion of theseat portion.

[0037] In the present invention, a region, whose elastic compliance whenthe reaction force is applied to the extending side of the cushionmaterial when an occupant is seated on the seat is smaller than that ofa human body portion pressing the cushion material and whose linearityof displacement is higher than that of the predetermined regionincluding a seat portion which a tuber ishiadicum bottom portion of anoccupant contacts, is provided at a seat portion which the vicinity of apelvis front portion of an occupant contacts, between the predeterminedregion including a seat portion which a tuber ishiadicum bottom portionof an occupant contacts, and a front edge portion of the seat portion.Accordingly, slidability of buttocks can be reduced, and seatingstability when an occupant is seated can be improved.

[0038] When the three-dimensional knitted fabric is stretched across theseat frame, a seat surface rear end portion of the predetermined regionincluding a seat portion which a tuber ishiadicum bottom portion of anoccupant contacts is slackened to a predetermined amount. However, aseat portion which the vicinity of a pelvis front portion of an occupantcontacts, between the predetermined region including the seat portionwhich a tuber ishiadicum bottom portion of an occupant contacts, and afront edge portion of the seat portion is hardly slackened. In thiscase, the three-dimensional knitted fabric is stretched across the seatframe such that a portion from the rear end of the seat portion to thepredetermined region of the seat which a tuber ishiadicum bottom portioncontacts is slackened by an extra width of 5 to 60 mm in relation to theentire width of the seat frame for structuring the seat portion. On theother hand, the portion of the seat portion which the vicinity of apelvis front portion contacts, between the predetermined region of theseat which a tuber ishiadicum bottom portion contacts and the front edgeportion of the seat portion is slackened by leaving an extra width of 0to 20 mm.

[0039] The elastic member comprises a mesh-structure elastic member, asheet-structure elastic member, or a mesh or sheet-structure elasticmember supported by a metal spring, an elastic member which can impartlarge elasticity to a seat portion which the vicinity of a pelvis frontportion of a seat occupant contacts.

[0040] Next, the three-dimensional knitted fabric will be explained.

[0041] The three-dimensional knitted fabric further comprises a portionwhich has a high surface stiffness, and a main elastic region which hasa low surface stiffness and accordingly, imparts a major restoring forcein relation to compressive deformation. In this case, two regions ormore each having different compressibility are provided at thethree-dimensional knitted fabric, and among these regions, one region,whose compressibility is high, is structured as the main elastic regionimparting a major restoring force in relation to compressivedeformation.

[0042] The three-dimensional knitted fabric has a main elastic regionwhich has compressibility in a range from 20 to 90%, and compressiveelasticity in a range from 75 to 100%, and compressibility differencebetween the main elastic region and a non-main elastic region is 5% ormore.

[0043] Recesses and projections are formed at least one of the surfacesof the three-dimensional knitted fabric, either the recesses or theprojections are formed as the main elastic region. In this case, theprojections are formed among adjacent recesses into substantiallyarch-shaped cross sections to structure the main elastic region bymaking use of elasticity in a bending direction of the projectionshaving substantially arch-shaped cross sections.

[0044] The three-dimensional knitted fabric is stretched across the seatframe such that the projections are formed in a wale form in anarbitrary direction of a surface of the three-dimensional knittedfabric, and the projections run in a longitudinal directioncorresponding to a left-right direction of the seat at a seat portion orboth at a seat portion and a back portion.

[0045] When projections of the three-dimensional knitted fabric arearranged in a lattice form or a staggered form, it is preferable thatthe three dimensional knitted fabric be stretched across the seat framesuch that a direction in which arrangement density of the main elasticregion is high corresponds to a left-right (transverse) direction of theseat at a seat portion alone or both at a seat portion and a backportion.

[0046] The three-dimensional knitted fabric is stretched across the seatframe at an elongation percentage of 5% or less. A thickness of the mainelastic region of the three-dimensional knitted fabric ranges from 5 to80 mm. A percentage per unit area of the main elastic region of thethree-dimensional knitted fabric when projected on a plane can be 30%/m²to 90%/m².

[0047] The main elastic region of the three-dimensional knitted fabricis formed by adjusting a knitting organization of the three-dimensionalknitted fabric and is adjusted by any one element or by combining twoelements or more of a group of elements comprising a connecting threadarrangement density, a connecting thread thickness, a connecting threadlength, a connecting thread material, a ground knit fabric mesh shape, aground knit fabric mesh size, a ground thread material for structuringthe ground knit fabric, and a mesh tightness at the connecting portionof the connecting threads and a ground knit fabric.

[0048] Further, recesses can be formed by joining the connecting threadsbetween the pair of ground knit fabrics in a state in which they aremade to approach one another, and projections structure the main elasticregion. The recesses of the three-dimensional knitted fabric are formedby one of welding, adhesion, stitching, welding using molten fabric, andvibration welding.

[0049] Moreover, in the three-dimensional knitted fabric can be formedin a region of projections and a region of recesses with differentelements by changing one or two or more of a group of elementscomprising a connection thread arrangement density, a connecting threadthickness, a connecting thread length, a connecting thread material, aground knit fabric mesh shape, a ground knit fabric mesh size, a groundthread material for structuring the ground knit fabric, and a meshtightness at a connecting portion of the connecting threads and a groundknit fabric.

[0050] The three-dimensional knitted fabric can be formed such that theconnecting threads in the recesses have an arrangement density lowerthan that of the connecting threads in the projections for structuringthe main elastic region.

[0051] The pair of ground knit fabrics, which are disposed so as to beseparated from one another, comprising a first ground knit fabric whichis formed by a flat fabric organization, and a second ground knit fabricwhich comprises a plurality of strip-shaped knit fabric portionsarranged so as to extend in a predetermined direction at a predeterminedspacing, wherein the three-dimensional knitted fabric is formed byconnecting a plurality of the strip-shaped knit fabric portions,respectively, to the first ground knit fabric, with connecting threadsat a region of the first ground knit fabric which faces respectivestrip-shaped fabric portions, at a region of the first ground knitfabric which faces respective cylinders among the respectivestrip-shaped fabric portions, and at a region of the first ground knitfabric which faces other adjacent strip-shaped fabric portions. In thethree-dimensional knitted fabric thus structured, the strip-shaped knitfabric portions connected with connecting threads form wale-shapedprojections.

[0052] The present invention further comprises a hollow portion whereconnecting threads have been removed, the hollow portion formed at awidthwise intermediate portion of a region where the first ground knitfabric faces the strip-shaped knit fabric portions. The respective edgeportions of the strip-shaped knit fabric portions and the first groundknit fabric are made to approach one another so that the respectivestrip-shaped knit fabric portions form projections. Due to thisstructure, elastic compliance of the three-dimensional knitted fabriccan be increased.

[0053] The present invention further comprises a plurality ofcommunicating portions where the respective adjacent strip-shaped knitfabric portions link with each other at a plurality of portionsseparated from one another at a predetermined spacing in an extendingdirection of the strip-shaped knit fabric portions.

[0054] It is preferable that the three-dimensional knitted fabricapplicable to the present invention have substantially the same value asthat of a human body portion pressing the cushion material.

[0055] As described above, the cushion material comprises a first regionwhose elastic compliance when a reaction force is applied to anextending side of the cushion material when an occupant is seated on theseat is substantially equivalent to that of a human body portionpressing the cushion material, and a second region whose elasticcompliance is greater than that of the first region.

[0056] Consequently, in accordance with the present invention, a thinand light seat can be provided, load concentration on a tuber ishiadicumbottom portion of a seat occupant can be mitigated, and accordingly,riding comfort can be improved, when an occupant is seated for a longperiod of time, numbness can be reduced, and vibration-transmittingcharacteristics can be mitigated.

[0057] Further, if the elastic compliance of a front edge portion of aseat portion when a reaction force is applied to an extending side ofthe cushion material is made larger than that of a seat portion whichthe vicinity of a tuber ishiadicum bottom portion of a seated occupantcontacts, the impeding of blood flow into the thighs of a seatedoccupant can be prevented, and when the cushion material is used for avehicle seat, smooth pedal operation can be facilitated.

[0058] Moreover, by raising the linearity of the elastic compliancecharacteristic of a seat portion which a pelvis front portion of aseated occupant contacts, when a reaction force is applied to anextending side of the cushion material, and by making the elasticcompliance of the seat portion which a pelvis front portion of theseated occupant contacts less than that of the seat portion which atuber ishiadicum bottom portion (a predetermined region including atuber ishiadicum bottom portion) of a seated occupant contacts,slidability of the buttocks of a seated occupant is minimized, andseating stability can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

[0059]FIG. 1 is a perspective view of a seat, a portion of which is cutaway, according to an embodiment of the present invention;

[0060]FIG. 2 is a cross-sectional view of the seat cut along the lineA-A.

[0061]FIG. 3 is a perspective view of another stretching state of athree-dimensional knitted fabric for constituting an upper elasticmember and a cushion material for a back portion;

[0062]FIG. 4 is a view of a simple model of the cushion material forexplaining an operation of a load applied to the cushion material;

[0063]FIG. 5 shows a structure of a three-dimensional knitted fabric ofa first embodiment of the present invention according to the presentembodiment;

[0064]FIG. 6 shows an example of one ground knit fabric;

[0065]FIG. 7 shows an example of the other ground knit fabric;

[0066]FIGS. 8A to 8E show examples of various types of arrangement ofconnecting threads;

[0067]FIG. 9 is a perspective view of a structure of a third embodimentof the three-dimensional knitted fabric according to the presentembodiment;

[0068]FIG. 10 is a cross-sectional view of FIG. 9;

[0069]FIG. 11 is a plan view of FIG. 9;

[0070]FIG. 12 is a view of an example of one ground knit fabric of thethird embodiment;

[0071]FIG. 13 is a perspective view of a fourth embodiment of thethree-dimensional knitted fabric comprising recesses and projectionsthat can be used as the upper elastic member according to the presentembodiment;

[0072]FIG. 14 is a cross-sectional view of the three-dimensional knittedfabric shown in FIG. 13;

[0073]FIG. 15 is a schematic view for explaining an operation ofsubstantially arch-shaped spring elements formed on thethree-dimensional knitted fabric shown in FIG. 13;

[0074]FIG. 16 is a schematic view for explaining an operation ofsubstantially arch-shaped spring elements formed on thethree-dimensional knitted fabric shown in FIG. 13;

[0075]FIG. 17 is a sectional view of a fifth embodiment of thethree-dimensional knitted fabric which can be applied to the presentembodiment;

[0076]FIG. 18 is a sectional view of a sixth embodiment of thethree-dimensional knitted fabric that can be applied to the presentembodiment;

[0077]FIG. 19 is a schematic view of an example of one ground knitfabric of the sixth embodiment;

[0078]FIG. 20 is a graph illustrating the relationship betweendisplacement and load (pressure) in Examples and Comparative Examples ofthe third to sixth embodiments of the three-dimensional knitted fabric;

[0079]FIG. 21 is a graph illustrating the relationship betweendisplacement and load at buttocks of a human body in Examples of thethird to sixth embodiments of the three-dimensional knitted fabric;

[0080]FIG. 22 is a graph illustrating elastic compliance of a human bodymeasured by using a pressurizing plate having a diameter of 98 mm;

[0081]FIG. 23 is a graph illustrating elastic compliance characteristicswhich is measured by using the 98 mm-diameter pressurizing plate at adistance of 150 mm from a seat surface rear end of a cushion materialfor a seat portion in Examples and Comparative Examples;

[0082]FIG. 24 is a graph illustrating elastic compliance characteristicsmeasured by using the 98 mm-diameter pressurizing plate at a distance of250 mm from the seat surface rear end of the cushion material for theseat portion in Examples and Comparative Examples;

[0083]FIG. 25 is a graph illustrating elastic compliance characteristicswhich is measured by using the 98 mm-diameter pressurizing plate at adistance of 350 mm from the seat surface rear end of the cushionmaterial for the seat portion in Examples and Comparative Examples;

[0084]FIG. 26 is a graph illustrating overlapping elastic compliancecharacteristics at distances of 150 mm and 250 mm from the seat surfacerear end of the cushion material for the seat portion in Examples;

[0085]FIG. 27 is a graph illustrating overlapping elastic compliancecharacteristics at distances of 150 mm and 250 mm from the seat surfacerear end of the cushion material for the seat portion in ComparativeExamples;

[0086]FIG. 28 is a graph illustrating vibration-transmittingcharacteristics of the seat in Examples;

[0087]FIG. 29 is a graph illustrating a comparison between verticalvibration-transmitting characteristics of the cushion material of theseat portion and those of a waist portion of a human body in relation toa floor;

[0088]FIG. 30A is a diagram of frequency characteristics of a springconstant k of a JM85;

[0089]FIG. 30B is a diagram of frequency characteristics of a dampingcoefficient c of a JM85;

[0090]FIG. 31 is a schematic view of a measuring apparatus of the springconstant k and the damping coefficient c of a JM85;

[0091]FIG. 32 is a schematic view of a vibration model with 1 degree offreedom, having the spring constant k and the damping coefficient c;

[0092]FIG. 33 is a graph showing a frequency characteristic of flexureof a muscle portion of the buttocks;

[0093]FIG. 34 is a graph showing an elastic compliance of the cushionmaterial by simulating the state in which a characteristic of a muscleportion and a characteristic of the cushion material are in equilibriumat distances of 150 mm and 250 mm from the seat surface rear end;

[0094]FIG. 35A is a graph showing a characteristic at 3 Hz by enlarginga portion A of FIG. 34;

[0095]FIG. 35B is a graph of a characteristic at 4 Hz;

[0096]FIG. 36 is a graph of static body pressure distribution of thecushion material;

[0097]FIG. 37 is a graph illustrating a Lissajous's waveform which isformed by a pressure value from the 98-diameter pressurizing plate andflexure of the cushion material;

[0098]FIG. 38A is a schematic plan view in which projections arearranged in a lattice form; and

[0099]FIG. 38B is a schematic plan view in which projections arearranged in a staggered form.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0100] With reference to accompanying drawings, a detailed descriptionof an embodiment of the present invention will be made, hereinafter.

[0101]FIG. 1 is a perspective view showing a structure of a seat 10according to an embodiment of the present invention, in which a portionhas been cut away.

[0102] As shown in FIG. 1, the seat 10 of the present embodimentcomprises a seat frame 20 and a cushion material 30 supported by theseat frame 20. The seat frame 20 further comprises a frame for a seatportion (seat cushion portion) 21 and a frame for a back portion (a seatback portion) 22. A cushion material for a seat portion 31 and a cushionmaterial for a back portion 32 are supported respectively by the framefor the seat portion 21 and the frame for the back portion 22. A seatportion (a cushion portion) 40 of the seat 10 of the present embodimentis supported by the frame for the seat portion 21 and the cushionmaterial for the seat portion 31. A back portion (seat back portion) 50of the seat 10 is formed by the frame for the back portion (seat backportion) 22 and the cushion material for the back portion 32.

[0103] Further, in the present embodiment, the frame for the backportion 22 can rotate forward and backward in relation to the frame forthe seat portion 21 around a supporting shaft 23, and a recliningmechanism is thereby formed.

[0104] As shown in FIGS. 1 and 2, the cushion material for the seatportion 31 comprises metal springs (coil springs) 31 a each having oneend supported by a side frame 21 a for forming the frame for the seatportion 21, and a mesh structure elastic member 31 b elasticallysupported by the other ends of the respective metal springs 31 a. Thecushion material for the seat portion 31 further comprises anintermediate elastic member 31 c which is laminated on a top surface ofthe mesh structure elastic member 31 b, and an upper elastic member 31 blaminated on a top surface of the intermediate elastic member 31 c andstretched between a pair of side frames 21 a facing one another. In thepresent embodiment, the intermediate elastic member 31 c and the upperelastic member 31 d are respectively formed by the three-dimensionalknitted fabric. The intermediate elastic member 31 c is provided for thepurpose of suppressing a sensation of having hit the bottom felt whenusing only the upper elastic member 31 d, and for mitigating a foreignmatter sensation caused by the mesh structure elastic member 31 b andthe metal spring 31 a. Of course, it is possible to use the upperelastic member 31 d in a single layer without folding thethree-dimensional knitted fabric. However, as shown in FIG. 1, theforeign matter sensation caused by the metal springs 31 a and the likecan further be mitigated by folding the three-dimensional knitted fabricat both sides of the side frame 21 a.

[0105] Depending on the thickness of the three-dimensional knittedfabric as the upper elastic member 31 d, there are of course cases whenthe intermediate elastic member 31 c need not be provided. Further, asthe mesh structure elastic member 31 b, Plumaflex (product name) orcontour mat (product name) can be used. However, instead of the meshstructure elastic member 31 b, a sheet structure elastic member can beused. The sheet structure elastic member is formed by a two-dimensionalor a three-dimensional fabric or knitted fabric structured by threadshaving a spring constant which imparts high linearity. If the sheetstructure elastic member or the mesh structure elastic member canindependently impart elasticity equivalent to that in the presentembodiment in which the metal springs 31 a are used, the metal springsneed not be used, and the mesh structure elastic member or the sheetstructure elastic member can be connected directly to the side frame 21a.

[0106] As shown in FIG. 1, only the upper elastic member 31 d which isformed by the three-dimensional knitted fabric is disposed by beingstretched and supported by the side frames 21 a and a front end frame 21b in the vicinity of a front edge portion 41 of the seat portion 40 (ata position of 350 mm from the seat surface rear end) of the presentembodiment, and accordingly, no other elastic member (i.e., lowerelastic member) such as the mesh structure elastic member 31 b or thelike for structuring the cushion material for the seat portion 31 isprovided. In other words, a lower elastic member comprising the meshstructure elastic member 31 b or the metal springs (coil springs) 31 ais disposed between the vicinity of a tuber ishiadicum bottom portionand the front edge portion 41 of the seat portion, which is a regionthat excludes the vicinity of the front edge portion 41 and arearward-direction portion from the vicinity of a tuber ishiadicumbottom portion.

[0107] When an occupant is seated, a region of a seat portioncorresponding to the vicinity of a tuber ishiadicum bottom portion of aseated occupant (a predetermined region including the seat portion,which a tuber ishiadicum bottom portion of a seated occupant contacts)has a lower elastic member beneath the three-dimensional knitted fabric,and is positioned at a region in the vicinity of a border between theregion including the lower elastic member and the region excluding thelower elastic member. Accordingly, the three-dimensional knitted fabricis structured such that the region where the lower elastic member hasbeen removed (where only the three-dimensional knitted fabric exists)and the region where both the three-dimensional knitted fabric and thelower elastic member co-exist react with one another, and thethree-dimensional knitted fabric has an elastic compliance substantiallyequivalent to that of a portion of an occupant's body contacting thecushion material.

[0108] A lower elastic member such as the mesh structure elastic member31 b does not exist in the vicinity under the front edge portion 41 ofthe seat portion. Accordingly, when an occupant is seated on the seat, aspring constant of the front edge portion 41 when a reaction force isapplied to an extending side of the seat portion (i.e., a reaction forcein a pressing direction along the thighs of a seated occupant) issmaller than that of the other region in which the lower elastic membersuch as the mesh structure elastic member 31 b exist). In other words,the vicinity of the front edge portion 41 imparts a greater elasticcompliance when a reaction force is applied to the extending side of theseat portion, and tends to operate as a damping element. Consequently, areaction force pressing rear sides of the thighs of a seated occupantbecomes smaller preventing the impeding of blood flow into the thighs,and when the cushion material is used for a vehicle seat, it is possibleto facilitate a smooth pedal operation.

[0109] The elastic compliance of the vicinity of the front edge portion41 is larger than that of a remaining region of the seat portion, andaccordingly, is larger than that of a human body portion pressing thevicinity of the front edge portion 41 of the seat portion.

[0110] A region 42 of the seat portion which the vicinity of a pelvisfront portion of the seat occupant contacts, between the seat portionwhich the vicinity of a tuber ishiadicum bottom portion of a seatedoccupant contacts, and a front edge portion of a seat portion (at aposition of 100 mm in front of a tuber ishiadicum bottom portion) ispositioned at a substantially central portion (including the centralportion and a portion for-ward from the central portion) of a region ofthe seat portion. Namely, the region of the seat portion including theregion 42 beneath the three-dimensional knitted fabric, has a lowerelastic member such as the mesh structure elastic member 31 b whichimparts a substantially linear elastic compliance characteristic when anoccupant is seated on the seat. For this reason, when a reaction forceis applied to an extending side of the cushion material, the region 42of the seat portion which the vicinity of a pelvis front portion of aseated occupant contacts, imparts an elastic compliance less than thatof a human body portion contacting the cushion material, and deformswith a higher linearity than that of the seat portion which the vicinityof a tuber ishiadicum portion of a seated occupant and a region rearwardtherefrom contact. Accordingly, a spring characteristic of the region 42of the seat portion which the vicinity of a pelvis front portion of aseat occupant contacts becomes greater, and the ishium portion of ahuman body positioned rearward of the vicinity of a pelvis front portioncan largely sink into the seat cushion without stretching thethree-dimensional knitted fabric itself at a large seat angle (angle ofa seat cushion in relation to a normal line). Accordingly, rotation ofthe seat portion which an ishium portion of a seated occupant contactsis prevented, and stability of seating posture can be improved.

[0111] More specifically, a lower elastic member such as the meshstructure elastic member 31 b is disposed within a range of 100 to 300mm forward from the seating surface rear end of the seat portion so asto impart to a considerable extent high linear elastic compliance to theregion 42 of the seat portion which a pelvis front portion of a seatedoccupant contacts, by adjustments of size, shape, attachment angle, andattachment position.

[0112] A driver needs to stabilize a seating posture in order to drive acar. Therefore, when a seating angle is increased, a load outputted fromthe buttocks (ishium) to a waist portion generally becomes larger. Inthe seat of the present embodiment, the three-dimensional knitted fabric(net) need not be tensely stretched to increase the seating angle. Byremoving a lower elastic member such as a mesh structure elastic memberor the metal spring from the seat portion which a tuber ishiadicumbottom portion of a seated occupant contacts, and a rearward-directionportion therefrom, a reaction force applied to the seat portion whichthe ishium contacts is made smaller than that applied to the seatportion which a pelvis front portion contacts. Consequently, when anoccupant is seated on the seat, an ishium of a seated occupant can sinkin more deeply, producing a similar effect to a case when a largeseating angle is formed.

[0113] Namely, in the present embodiment, the cushion material is formedby using a three-dimensional knitted fabric which has a springcharacteristic approximate to that of a muscle portion of a human bodyand a lower elastic member which is smaller than the three-dimensionalknitted fabric and whose elastic compliance characteristic issubstantially linear. The three-dimensional knitted fabric is stretchedacross the seat frame and is mounted on the lower elastic member. Anelastic compliance of a region (second region) at which the lowerelastic member beneath the three-dimensional knitted fabric is greaterthan that of a human body portion contacting the seat. An elasticcompliance of a region at which the lower elastic member exists beneaththe three-dimensional knitted fabric, i.e., a region (first region)which is disposed near a border between the region including the lowerelastic member and the region excluding the lower elastic member,beneath the three dimensional knitted fabric is substantially equivalentto that of a human body portion contacting the cushion material.Accordingly, an elastic compliance of a region including the lowerelastic member beneath the three-dimensional knitted fabric, i.e., aregion between the first region and the second region is less than thatof a human body portion contacting the seat.

[0114] The lower elastic member is preferably positioned at a region ofthe seat portion which both a tuber ishiadicum bottom portion of anoccupant and a forward-direction portion therefrom contact, a regionexcluding the front edge portion of the seat portion which the thighs ofa human body (seated occupant) contact.

[0115] The cushion material for the back portion 32 is formed by athree-dimensional knitted fabric and is stretched between the sideframes 22 a of the frame for the back portion 22. In this way, thecushion material for the back portion 32 is structured only by thethree-dimensional knitted fabric, imparts a small restoring force, andhas a large damping characteristic. For this reason, the cushionmaterial for the back portion 32 is easily deformed in order to followchanges in the posture of a seated occupant. A lower portion of thethree-dimensional knitted fabric for forming the cushion material forthe back portion 32 and a rear portion of the three-dimensional knittedfabric for structuring the upper elastic member 31 d of the cushionmaterial for the seat portion 31 are sewn together. As a result, aregion from the buttocks to a waist portion of a seated occupant, whichis where a great load is applied when an occupant is seated, issupported in a hammock-like manner such that a body of a seated occupantis raised up from buttocks to the waist portion. In this way, theforeign matter sensation arising from various frame members, arranged ina rearward-direction from the region of the buttocks to the waistportion, can be mitigated, it becomes easier for the seat to followchanges in the posture of a seated occupant, and the sensation ofsitting can be improved.

[0116] Thus, a vibration model at 2 degrees of freedom having a dynamicvibration absorption effect is formed by a mass of thighs and an elasticcompliance of the three-dimensional knitted fabric under the thighs of aseated occupant. The vibration model at 2 degrees of freedom, vibrationdue to the mass of thighs and the vibration of the three dimensionalknitted fabric under the thighs can reduce a vibration characteristicgain of a main vibration within a range of 4 to 6 Hz equivalent to aspring constant of a lower elastic member provided beneath thethree-dimensional knitted fabric which a tuber ishiadicum bottom portionof a seated occupant contacts, and which has an elastic compliancesmaller than that of the three-dimensional knitted fabric.

[0117] As shown in FIG. 3, both side portions of the upper elasticmember 31 d formed by the three-dimensional knitted fabric of thecushion material for the seat portion 31, and the cushion material forthe back portion 32 which is also formed by the three-dimensionalknitted fabric are respectively sewn together with fabric materials 31 eand 32 de such as felts, and the fabrics 31 e and 32 e can be stretchedso as to cover the side frames 21 a and 22 a. Accordingly, elongation ofthe three-dimensional knitted fabric in a transverse direction(left-light direction of the side frame) is suppressed, and elongationof the three-dimensional knitted fabric in a front-back directionbecomes larger. Accordingly, holding performance can be improved, andstability when an occupant is seated can be improved. A description ofthese effects will be made later.

[0118] Thus, the cushion material for the seat portion 31 and thecushion material for the back portion 32 provided as described above areset so as to form a tendency substantially equivalent to the elasticcompliance of a human body portion contacting the cushion material.However, such characteristics are achieved by using thethree-dimensional knitted fabric. The three-dimensional knitted fabricis formed by a pair of ground knit fabrics which are disposed so as tobe separated from one another and then joined together by connectingthreads, and is structured to support a load applied thereto bydeformation of a mesh which forms each of the ground knit fabrics,deformation (collapsing or buckling) of the connecting threads, and arestoring force of the adjacent connecting threads which imparts aspring characteristic to the deformed connecting threads. Accordingly,when an area of contact between an occupant and the cushion material islarge, due to a large reaction force imparted by a large number of theconnecting threads corresponding to the area, a large surface stiffnessis exerted. On the other hand, when a partial load is applied to theseat portion as in a case in which the thighs of the seat occupantcontacts the seat portion, namely, when an area of contact between aseated occupant and the cushion material is small, the number of theconnecting threads within the area of contact is small, and therestoring force imparted by the connecting threads, which support oneanother and prevent mutual deformation (collapsing or buckling) of theconnecting threads, is diminished. Consequently, the elastic complianceof the three-dimensional knitted fabric, as its own elastic compliancecharacteristic, is substantially approximate to that of a human bodyportion contacting a seat portion, and has a fluctuation characteristicin which an initial flexure amount is substantial, hysteresis isexperienced and accordingly, restoration insufficient.

[0119] As shown in FIGS. 1 and 2, a seat having such an elasticcompliance as described above has a specific structure in which one ofthe ends of the coil springs 31 a is supported by the side frames 21 afor structuring the frame 21 for the seat portion of the cushionmaterial 31, and the mesh structure elastic member 31 b formed by acontour mat or the like is supported by the other ends of the coilsprings 31 a. Then, as the intermediate plastic member 31 c, viscousurethane having a thickness of 10 mm, for example, is mounted on themesh structure elastic member 31 b, and urethane slub is furtherlaminated thereon. Finally, a conventional three-dimensional knittedfabric having a thickness of 1.3 mm is disposed on this.

[0120]FIG. 37 shows a Lissajous's waveform of a relationship between apressure value applied to the cushion material by using the pressurizingplate having a diameter of 98 mm (hereinafter, 98 mm-diameter pressuringplate), and a flexure amount of the cushion material. As is apparentfrom this graph, an elastic compliance characteristic of the cushionmaterial at a distance of 150 mm in front of the seat surface rear end(50 mm ahead of the rear end of the lower elastic member) issubstantially equivalent to that of a human body. Further, an elasticcompliance characteristic of the seat portion (cushion material) at adistance of 250 mm (50 mm to the rear from the front end portion of thelower elastic member of the seat portion which the vicinity of a pelvisfront portion of a seat occupant contacts) is less than that of a humanbody.

[0121] In this seat, three regions comprising a large elasticcompliance, a medium elastic compliance and a small elastic complianceare distributed in that order from the vicinity of a front edge portionof a seat portion to the seat surface rear end. A region of a largeelastic compliance corresponds to the vicinity of a front edge portionof the seat, a region of small elastic compliance corresponds to thevicinity of a pelvis front portion, and a region of medium elasticcompliance corresponds to the vicinity of a tuber ishiadicum bottomportion.

[0122] Since the three-dimensional knitted fabric operates as describedabove, the cushion material for the seat portion 31 of the presentembodiment is structured such that the upper elastic member 31 d whichis a member which imparts a spring characteristic substantiallyequivalent to a characteristic of a muscle portion of a human body isdisposed on the aforementioned mesh structure elastic member 31 b or thelike which has a spring constant whose linearity is high in relation tothe deformation of the cushion material. Accordingly, if a spring forcehaving high linearity such as the mesh structure elastic member 31 b anda weight of an occupant (vehicle occupant) are in equilibrium, when anexternal vibration is applied to a seated occupant from the seat cushionand a backrest (seat cushion for the back portion), a vibration system,which comprises a spring constant of the seat cushion and a mass of ahuman body, causes a vertical oscillation to a human body. Thepositioning energy due to flexure of spring when the weight of anoccupant and a spring force of the mesh structure elastic member 31 b ofthe cushion or the upper elastic member 31 d which is formed by thethree-dimensional knitted fabric are in equilibrium is converted into akinetic energy through a vibration of the mass of a human body when anexternal force is applied to a human body. The kinetic energy acts onthe cushion material in an anti-gravity direction, causes acceleration,and thereby mitigates gravity acceleration. Accordingly, the loadapplied to the cushion material is distributed. Consequently, flexurerestoration of the upper elastic member 31 d which is formed by thethree-dimensional knitted fabric, which has a smaller spring constantthan that of the mesh structure elastic member 31 b, becomes larger thanthat of the mesh structure elastic member 31 b. Namely, since thethree-dimensional knitted fabric whose spring constant is substantiallyequivalent to that of a muscle portion of an occupant reacts in relationto vibration, a muscle portion hardly flex, and vibration stimulusapplied to a human body is minimized (see FIG. 4).

[0123] As a result, the seat using the three-dimensional knitted fabricof the present embodiment can exhibit two spring characteristicscomprising a spring characteristic which has high linearity in relationto deformation (elastic compliance characteristic with high linearity),and a soft spring characteristic that is substantially equivalent tothat of a muscle portion of a human body (in particular, a muscleportion of the buttocks) and accordingly, imparts a considerable effectin alleviating vibration characteristics at a high frequency band.

[0124] As described above, the three-dimensional knitted fabric isformed by joining the pair of the ground knit fabrics disposed so as tobe separated from one another, with the connecting threads. Accordingly,the three-dimensional knitted fabric tends to exhibit a spring constantcharacteristic which is substantially equivalent to that of a muscleportion by adjusting any one element or by combining two elements ormore of a group of elements comprising: a connecting thread arrangementdensity, a connecting thread thickness, a connecting thread length, aconnecting thread material, a ground knit fabric mesh shape, a groundknit fabric mesh size, a ground thread material for structuring theground knit fabric, and a mesh tightness at the connecting portion ofthe connecting thread and the ground knit fabric.

[0125] Therefore, by using the three-dimensional knitted fabric togetherwith a lower elastic member such as a mesh structure elastic memberwhich deforms substantially linearly, it is possible to form a cushionmaterial with a spring constant smaller than that of a muscle portion(elastic compliance larger than that of a muscle portion), and a springconstant greater than that of a muscle portion (elastic compliancesmaller than that of a muscle portion).

[0126] The three-dimensional knitted fabric is used by being stretchedacross the seat frame, more specifically, the side frames 21 a and 22 a.Accordingly, each of the above-described characteristics is imparted ina state in which the three-dimensional knitted fabric is stretchedacross the seat frame. Further, as in the cushion material for the seatportion 31 of the above-described present embodiment, if a cushionmaterial has the lower elastic members such as the metal springs 31 aand the mesh structure elastic member 31 b, in addition to the upperelastic member 31 d which is formed by the three-dimensional knittedfabric, these characteristics are all measured as characteristics of theentire cushion material for the seat portion 31.

[0127] In the above description, an example has been described in whicha second region whose elastic compliance is larger than that of a humanbody portion pressing the cushion material is positioned near a frontedge portion of the seat portion, and a first region whose elasticcompliance is substantially equivalent to that of an occupant's bodyportion pressing the cushion material is positioned at the seat portionwhich the vicinity of a tuber ishiadicum bottom portion of a seatedoccupant contacts. However, the first region and the second region canbe laminated to each other such that the second region is positioned ona top surface layer portion of the seat portion. By laminating the firstregion and the second region to one another, vibration is transmitted toa human body through a region of the seat portion which has an elasticcompliance greater than that of a muscle portion of a human body.Accordingly, vibration stimulus can be mitigated, and riding comfort canbe improved.

[0128] Further, besides the fact that the first region and the secondregion can be laminated to one another so that the second region ispositioned on a top surface layer, the laminated portion of the firstand second regions is positioned at the seat portion which the vicinityof a tuber ishiadicum bottom portion of a seated occupant contacts, anda region, from which the laminated portion has been removed, and whichhas an elastic compliance larger than that of a human body portionpressing thc cushion material is positioned at thc front edge portion ofthe seat portion. Accordingly, vibration stimulus to a human body ismitigated, riding comfort can be improved, and numbness of a muscleportion in the vicinity of a tuber ishiadicum bottom portion and theimpeding of blood flow into the thighs of a seated occupant can beprevented.

[0129] Embodiments of the Three-Dimensional Knitted Fabric

[0130] A description of an embodiment of the three-dimensional knittedfabric 100 used for the upper elastic member 31 d of the cushionmaterial for the seat portion 31 and for the cushion material for theback portion 32 according to the above-described embodiment of thepresent invention will be made hereinafter.

[0131] The terms “compressibility and compressive elasticity” used inthe following explanation are measured by a test method on the basis of“Compressibility and compressive elasticity” in JASO standard-M404-84.More specifically, a thickness to (mm) of each of three sample sheets,which are cut into 50 mm x50 mm, is measured when an initial load of 3.5g/cm² (0.343 kPa) is applied thereto in a thickness direction of eachsample sheet for thirty seconds. Then, a thickness t₁ (mm) of eachsample sheet is measured when a load of 200 g/cm² (19.6 kPa) is appliedthereto and left alone for ten minutes. Next, after sample sheets towhich no load is applied are left alone for ten minutes, a thickness t′₀(mm) of each sample sheet is measured when an initial load of 3.5 g/cm²(0.343 kPa) is again applied thereto for thirty seconds. Accordingly,compressibility and compressive elasticity are determined by thefollowing equations, and represented by a mean value of these samplesheets. Further, in respective manufacturing examples to be describedlater, compressibility and compressive elasticity of thethree-dimensional knitted fabrics, which have projections (waleportions) and recesses (portions except for the wale portions), aremeasured by each of the three-dimensional knitted fabrics being cut into50 mm×50 mm sheet samples. The compressibility and compressiveelasticity of the three-dimensional knitted fabrics obtained are used asdata for projections (or wale portions) as a main elastic region.Compressibility of the recesses (or portions other than projections) ismeasured by cutting into 50 mm×50 mm sample sheet each of thethree-dimensional knitted fabrics, which are manufactured in the samemanner as the projections except that spacing between the projections(wale portions) is set at 50 mm:

Compressibility (%)={(t ₀ −t ₁)/t ₀}×100  (1)

Compressive elasticity (%)={(t′ ₀ −t ₁)/(t ₀ −t ₁)}×100  (2)

[0132] (First Embodiment)

[0133] With reference to FIGS. 5 to 8, a description of a firstembodiment of the present invention will be made hereinafter. As shownin FIG. 5, this three-dimensional knitted fabric 100 is structured by athree-dimensional structure that comprises a pair of ground knit fabrics110 and 120 which are disposed so as to be separated from each other,and a large number of connection threads 130 which run back and forthbetween a pair of the ground knit fabrics 110 and 120 so as to join themtogether.

[0134] As shown in FIG. 6, the first ground knit fabric 110 can beformed, for example, by using a fabric which forms a mesh by a flat knitfabric organization (small cylinders) which uses threads formed bytwisting short fibers, and which is continuous in both the waledirection and the course direction. Conversely, as shown in FIG. 7, theother ground knit fabric 120 can be formed into a knit fabricorganization whose cylinders are larger than the first ground knitfabric 110, for example, by using a fabric which forms a honeycomb(hexagonal) mesh using threads formed by twisting short fibers. This ismerely one example, and knit fabric organizations other than a smallstitch knit fabric organization or a honeycomb mesh can be used. Theconnecting threads 130 are woven in between the pair of ground knitfabrics 110 and 120 so that a predetermined spacing is maintainedbetween the first ground knit fabric 110 and the other ground knitfabric 120. In this way, a predetermined stiffness is imparted to thethree-dimensional knitted fabric 100 which is mesh knit.

[0135] The three-dimensional knitted fabric 100 can provide the requiredstiffness, depending on the thickness of the ground threads forming theground knit fabrics 110, 120, and the like. However, it is preferablethat the ground threads be chosen from a range which does not make theknitting difficult. Further, monofilament threads can be used as theground threads. Multfilament threads or spun threads may be used inconsideration of the feel, the softness of the surface tactilesensation, and the like.

[0136] Monofilament threads are preferably used as the connectingthreads 130, and their thickness is preferably in the range of 167decitex to 1100 decitex. With multifilament threads, a cushioningability having a good restoring force cannot be obtained. Moreover, ifthe thickness is less than 167 decitex, the stiffness of thethree-dimensional knitted fabric 100 becomes difficult to achieve. Ifthe thickness exceeds 1100 decitex, the three-dimensional knitted fabric100 will be too hard and proper cushioning ability cannot be achieved.In other words, by using monofilament threads of 167 decitex to 1100decitex as the connecting threads 130, the load of an occupant seated onthe seat can be supported by the deformation of the meshes forming theground knit fabrics 110, 120, the deformation caused by the collapsingor buckling of the connecting threads 130, and the restoring forces ofthe adjacent connecting threads 130 which impart a spring characteristicto the deformed connecting threads 130. A soft structure, which has asoft spring characteristic and in which stress concentration does notoccur, can be obtained. Further, as will be described later, when suchrecesses and projections are formed, spring elements which havesubstantially arch-shaped cross sections can be formed at thethree-dimensional knitted fabric. Thus, a soft spring characteristic canbe imparted, and a structure having an elastic compliance equivalent toor greater than that of a muscle portion can easily be formed.

[0137] The materials of the ground threads and the connecting threads130 are not particularly limited. Examples thereof are synthetic fibersand regenerated fibers such as polypropylene, polyester, polyamide,polyacrylonitrile, rayon, and the like, as well as natural fibers suchas wool, silk, cotton, and the like. A single type of this material maybe used, or plural types thereof may be used together in arbitrarycombinations. Preferably, thermoplastic polyester fibers such aspolyethylene terephthalate (PET), polybutylene terephthalate (PBT) andthe like, and polyolefin fibers such as nylon 6 and the like, andcombinations of two or more types of these fibers, are used. Further,polyester fibers are excellent in recyclic performance, which ispreferable. Moreover, the thread configurations of the ground threadsand the connecting threads 130 are not limited to those described above,and threads having circular cross-sections, threads having differentlyshaped cross-sections, or the like may be used.

[0138] Arrangements (pile organization) of the connecting threads 130 inwhich the connecting threads 130 join the ground knit fabrics 110, 120together can be described from a side view position. More specifically,for example, they can be divided into various arrangement types shown inFIGS. 8A to 8E. FIGS. 8A and 8B show straight types of the connectingthreads in which the connecting threads 130 are woven substantiallyupright in between the ground knit fabrics 110, 120. Of these, FIG. 8Ashows the connecting threads woven straight so as to form a numericalcharacter “8” shape, and FIG. 8B shows the connecting threads which aresimply woven straight. FIGS. 8C to 8E show a cross-type of theconnecting threads 130 which are cross-woven in between the ground knitfabrics 110, 120 at the respective intermediate points of the connectingthreads 130. Of these figures, FIG. 8C shows the connecting threads 130which are cross-woven and form a numerical character “8”, and FIG. 8Dshows the connecting threads 130 which are simply cross-woven. FIG. 8Eshows the connecting threads 130 each two of which are double-crosswoven. Further, as compared to a case in which the connecting threads130 are arranged substantially vertically in between the ground knitfabrics 110, 120 (see FIGS. 8A and 8B), as shown in FIGS. 8C to 8E inwhich the connecting threads 130 are inclined to cross each other, thisstructure can give soft spring characteristics of higher compressibilitywhile retaining a sufficient reaction force with the buckling strengthof the individual connecting threads 130.

[0139] (Second Embodiment)

[0140] In a second embodiment of the three-dimensional knitted fabric,the three-dimensional knitted fabric 100 according to theabove-mentioned first embodiment is manufactured so as to have recessesand projections in the same manner as a fifth embodiment which will bedescribed later and shown in FIG. 17. And the second embodiment will beexplained by using the reference numerals identical to those of FIG. 17.The three-dimensional knitted fabric 100 is manufactured such that apair of ground knit fabrics 330, 340 are disposed so as to approach toone another in a course direction at a predetermined spacing so thatrecesses 150 are formed, and projections 160 are formed among theadjacent recesses 150. This can easily provide the three-dimensionalknitted fabric with a structure which has a similar tendency to that ofa spring constant characteristic (elastic compliance) of a muscleportion of a human body, and a spring constant which is smaller thanthat of a muscle portion of a human body (an elastic compliance greaterthan that of a muscle portion of a human body).

[0141] Thus, when recesses and projections are formed on thethree-dimensional knitted fabric, the second region whose elasticcompliance is greater than that of a muscle portion of a human body isformed on a top surface layer portion of the three-dimensional knittedfabric. Under this second region, the first region whose elasticcompliance is substantially equivalent to that of a muscle portion of ahuman body can be formed.

[0142] The recesses 150 can be formed from just one of a pair of theground knit fabrics. However, as shown in FIG. 17, the recesses 150 canalso be formed at both sides of the pair of the ground knit fabrics.Examples of means for forming the recesses 150 by causing the groundknit fabrics to approach one another include: welding means, bondingmeans, as well as suture means by a sewing machine, and joining means bymelting molten fibers after interposing them in between the ground knitfabrics. Of these, use of vibration welding means is preferable becauseit can prevent a region to be welded from becoming rigid, and therebyimpart a high bonding strength.

[0143] In this way, by forming the recesses 150 on the three-dimensionalknitted fabric, the connecting threads 130, which are arranged within aregion at which the recesses 150 are formed, either incline or flex.Further, some of the connecting threads 130 move toward one side, to aregion of the projections 160, and the connecting threads 130 adjacentto each other are entangled (chain-crossed) and joined together. In thisway, when the connecting threads 130 are entangled and joined together,as schematically shown in FIG. 15, both side portions of the connectingthreads 130 between which entangled portions 130 a are interposed i.e.,projections of the three-dimensional knitted fabric, can respectivelyfunction as independent spring characteristics (deforming elements).Accordingly, as schematically shown in FIG. 15, a region extending fromanother entangled portion 130 a in which the connecting threads 130entangle in another recess 150 to another entangled portion 130 a inwhich the connecting threads 130 entangle in the adjacent recess 150adjacent to the above-mentioned recess 150, including the ground knitfabrics and the connecting threads 130 which are arranged in thisregion, is seemingly structured to form both one spring element having asubstantially arch-shaped cross section and a damping element due tofriction between the connections threads 130.

[0144] For this reason, in the three-dimensional knitted fabric havingrecesses and projections, elasticity of the recesses 150 and theprojections 160 are different from each other. When the projections 160are compressively deformed upon receiving a load, as compared to thecase in which the three-dimensional knitted fabric 100 on which recessesand projections are not formed, buckling strength becomes relativelylower, and a buckling characteristic is not easily exhibited. Therefore,as shown by an imaginary line in FIG. 15, elastic function of the springelement having a substantially arch-shaped cross section in a bendingdirection relatively becomes larger. Namely, as compared to thethree-dimensional knitted fabric which is formed under the sameconditions except that recesses and projections are not formed, a springcharacteristic of the projections 160 has a spring constant whichbecomes smaller (elastic compliance becomes larger), and at thebeginning, a very small load region becomes deformable, so that abuckling characteristic is not easily exhibited.

[0145] In the second embodiment of the present invention, as describedabove, the connecting threads 130 are entangled and joined together inthe recesses 150 so that elasticity, which extends and contracts in adirection substantially orthogonal to a line on which the recesses 150are formed, is imparted to the three-dimensional knitted fabric. Thus,when the three-dimensional knitted fabric is stretched between the seatframe, a spring performance which is imparted in a thickness directionby the spring elements which have substantially arch-shaped crosssections, and elasticity (spring performance) imparted in a planardirection substantially orthogonal to the thickness direction, thuscontributing to a decrease in spring constant, and an increase inelastic compliance.

[0146] It is preferable to stretch the three-dimensional knitted fabric100 of the second embodiment of the present invention across the seatframe at an elongation rate of 5% or less so as to sufficiently exhibitthe above-described characteristics. Further, as described above, inorder for the three-dimensional knitted fabric 100 to sufficientlyimpart such characteristics as described above to the seat portioncorresponding to the vicinity of a tuber ishiadicum bottom portion of aseated occupant and rear-ward therefrom, and impart spring performancehaving high linearity due to the mesh structure elastic member 31 b orthe like to the region 42 corresponding to the vicinity of a pelvisfront portion of an occupant, it is more preferable to stretch thethree-dimensional knitted fabric across the seat frame such that thethree-dimensional knitted fabric is slackened by leaving an extra widthof 5 to 60 mm of the seat frame, preferably, at a distance of 15 to 35mm from the seat surface rear end to the vicinity of a tuber ishiadicumbottom portion, i.e., at a distance of 100 to 150 mm from the seatsurface rear end, and by leaving an extra width which is infinitelyclose to zero, from the region 42 of the seat portion which correspondsto the vicinity of a pelvis front portion of an occupant at a distanceof about 200 to 300 mm from the seat surface rear end.

[0147] As shown in FIG. 3, at least at the seat portion, it ispreferable that the three-dimensional knitted fabric is stretched suchthat a longitudinal direction of the projections 160 (the recesses 150)corresponds to a left-right (transverse) direction (Y direction) of theseat. Namely, by stretching the three-dimensional knitted fabric likethis, due to elasticity which is caused in a planar direction which issubstantially orthogonal to the longitudinal direction of theprojections 160, the three-dimensional knitted fabric is likely toelongate in a front-back direction (X direction) of the seat.Accordingly, a shearing force which is applied to the longitudinaldirection of the seat becomes greater than that to the left-rightdirection of the seat, and a seating angle when an occupant is seated onthe seat becomes larger, whereby slidability of buttocks in a frontwarddirection of the seat can be inhibited and can improve the ability ofthe cushion material to follow the change of posture. Accordingly, whenthe three-dimensional knitted fabric is used for a driver's seat,stability of driving posture can be improved, and fatigue, affecting toa driver due to a driving for a long period, can be reduced. Further, asshown in FIG. 3, when the three-dimensional knitted fabric for the backportion is stretched in the same manner as in the seat portion such thatthe longitudinal direction of the projections 160 corresponds to theleft-right direction of the back portion. Accordingly, thethree-dimensional knitted fabric is likely to elongate in a verticaldirection (Z direction) of the back portion, thus helping the seatportion to flex, and further enabling the cushion material to follow achange of posture.

[0148] In the above description, an example in which a plurality ofprojections of the three-dimensional knitted fabric is arranged inparallel. However, the projections 160 of the three-dimensional knittedfabric can be arranged in a lattice form shown in FIG. 38A or in astaggered form shown in FIG. 38B. Also in this case, for the samereasons as described above, it is preferable to stretch thethree-dimensional knitted fabric across the seat frame such that, atleast at the seat portion, and more preferably, at both the seat portionand the back portion, projections arranged in a lattice form or in astaggered form and which have a larger dimension or a higher arrangementdensity, correspond to a transverse direction (Y direction) of the seat.

[0149] As shown in FIG. 16, at the time when the three-dimensionalknitted fabric 100 structured as described above contacts a regiondisturbed by human bones and represented by a mass M (substantiallyequivalent to a pressurizing plate having a diameter of 30 mm), theprojections 160 between which the recesses 150 are interposed arerecessed and deformed so as to seemingly escape outwardly, and causepartial fatigue. Namely, the projections deform in directions separatingfrom one another. Thereafter, when an additional load is applied to alarge area of the three-dimensional knitted fabric, the load issupported by the entire three-dimensional knitted fabric. However, byhaving such recesses and projections, the three-dimensional knittedfabric deforms as shown in FIG. 16, whereby a sensation of fitting canbe enhanced within a narrow displacement region.

[0150] The projections 160 correspond to a region having a largecompressibility which functions as a main elastic region whose surfacestiffness is low, and which mainly exhibits a restoring force inresponse to compressive deformation. The recesses 150 correspond to aregion which exhibits only slight elasticity in the thickness direction,has a small compressibility, and has a high surface stiffness. Further,the surface stiffness is determined by the degree of vertical deflection(thickness direction) and transverse direction (shear direction) of thethree-dimensional knitted fabric. A portion having large compressibilityis easily offset in both directions, and a portion having smallcompressibility does not deflect easily. Accordingly, the portion havinglarge compressibility tends to have a low surface stiffness, and aportion having small compressibility tends to have high surfacestiffness.

[0151] The projections 160 for forming the main elastic region arestructured as described above. Accordingly, white the projections 160impart large compressibility, they also impart the required restoringforce. When the three-dimensional knitted fabric having the projections160 are stretched between the seat frame and used as a cushion material,it becomes possible to impart a spring constant characteristic close tothat of a muscle portion of the buttocks. Namely, as an elasticcompliance characteristic which is caused when an occupant is seated onthe seat, and a reaction force is imparted from the elongated side ofthe seated portion, and projections having greater elastic compliancethan that of a human body portion contacting the seat cushion, andrecesses having elastic compliance which is substantially equivalent tothat of a human body portion contacting the seat cushion can be formed.

[0152] Thus, it is possible to prevent deformation of a muscle portionof the buttocks when an occupant is seated on the seat, and also toreduce a spring characteristic of the skin and a muscle portion of ahuman body, which can be a damping element in a vibration region of 6 Hzor more, especially 10 Hz or more.

[0153] In order for the three-dimensional knitted fabric 100 to impartthe above-described characteristics, it is preferable thatcompressibility of the projections 160 as a main elastic region is from20 to 90%, and compressive elasticity thereof be set within a range of75 to 100%. In the second embodiment of the present invention, it ispreferable that compressibility of projections other than theprojections for forming the main elastic region (the remainingprojections) be set such that a difference of compressibility betweenthe recesses 150 and the projections 160 is 5% or more.

[0154] (Third Embodiment)

[0155] With reference to FIGS. 9 to 12, a third embodiment of thepresent invention will be explained, hereinafter. A three-dimensionalknitted fabric 210 is structured by a pair of ground knit fabrics 220and 230, and the connection threads 130.

[0156] A pair of the ground knit fabrics 220 and 230 is disposed so asto be separated from one another, and the connecting threads 130 areprovided so as to run back and forth between the pair of the ground knitfabrics 220 and 230. The first ground knit fabric 220, as shown in FIG.9, is continuously woven meshes, extends in a wale direction, and hasstrip-shaped fabric portions 221 which are separated from each other byone or plural wales. As a result, cylinders 222 are formed among theadjacent strip-shaped fabric portions 221, and as shown in FIG. 10, therespective strip-shaped fabric portions 221, and the connection threads130 arranged in a region between the strip-shaped fabric portions andthe other ground knit fabric 220 constitute a part of wale portions 232which act as projections. The strip-shaped fabric portions 221 forforming the respective wale portions 232 can be provided independently.However, in order to improve a restoring force of the connecting threads130, it is preferable that communication portions 224, which link theadjacent strip-shaped fabric portions 221 so as to be cross-linked withone another, are provided at a predetermined spacing of one or severalcourses in a wale direction. FIGS. 9 and 11 show a state in which theadjacent strip-shaped fabric portions 221 are linked to one another bythe communicating portions 224.

[0157] The communicating portions 224 are not necessarily arranged inlattice-form, and instead, can be arranged in a staggered-form or anyother irregular form. On the other hand, as shown in FIG. 12, the otherground knit fabric 230 can be formed, for example, by a flat knit fabricorganization which is continuous both in a wale direction and a coursedirection. However, a knitting organization of the ground knit fabrics220 and 230 is not limited to that shown in this figure. For example, athrough hole organization such as a mesh or a tricot can be employed.

[0158] The connecting threads 130 are arranged so as to run back andforth between the ground knit fabrics 220 and 230 facing each other.More specifically, a portion of the connecting threads 130 is arrangedbetween the strip-shaped fabric portions 221 and the ground knit fabric230. Further, as shown in FIG. 10, a portion of the connecting threads130 which are connected to one of the strip-shaped fabric portions 221is connected to the ground knit fabric 230 at a region of the groundknit fabric 230 which front-faces the strip-shaped fabric portion 221.On the other hand, the other portion of the connecting threads 130 isconnected to the ground knit fabric 230 at a region of the ground knitfabric 230 which is positioned directly beneath the cell 222 adjacent tothe one strip-shaped fabric portion 221, and at a region of the groundknit fabric 230 which front-faces the other adjacent strip-shaped fabricportion 221.

[0159] As a result, the other portion of the connecting threads 130 isdiagonally arranged in between the ground knit fabrics 220 and 230.Further, in any one of the strip-shaped fabric portions 221, theconnecting threads 130 are arranged in this form so that the connectingthreads 130 cross each other at the lower portions of the cylinders 222between the adjacent strip-shaped fabric portions 221. Then, due to sucharrangement of the connecting threads 130, the three-dimensional knittedfabric can impart a soft spring characteristic having a largecompressibility as compared to the arrangement in which the entireconnecting threads 130 are arranged almost vertically in between theground knit fabrics 220 and 230 (see FIG. 5). Meanwhile, owing to abuckling strength of the respective connecting threads 130, thethree-dimensional knitted fabric can impart a soft spring feeling havingconsiderable compressibility, as well as sufficient restoring force.Further, in a third embodiment of the present invention, a hollowportion 241, where the connecting threads do not exist, is formed at awidthwise intermediate portion of each of the respective wale portions223 which are formed by the strip-shaped knit fabric portions 221 andthe connecting threads 130. Consequently, the three-dimensional knittedfabric can attain appreciably high compressibility and the hollowportion 241 also contributes to making the three-dimensional knittedfabric (cushion material) more compact.

[0160] The respective wale portions 223, which are formed by thestrip-shaped fabric portions 221 and the connecting threads 130according to the third embodiment of the present invention, operate as amain elastic region having low surface stiffness, which, in the samemanner as the projections 160, imparts a principal restoring force inrelation to compressive deformation. Further, the respective waleportions 223 are formed so as to be separated from one another at aspacing of one or a few wale portions, and thereby correspond to aportion of the main elastic region. In other words, as described above,the respective wale portions 223 are a region where the connectingthreads 130 cause a predetermined elasticity, and compressibility islarge. Further, a region comprising a portion of the connecting threads130 which are arranged directly under the cylinders 222 between the waleportions 223, and a portion of the other ground knit fabric 230 is wherethe arrangement density of the connecting threads 130 is lower than thatof the connecting threads in a region of the wale portions 223 formingthe main elastic region. A region which has a small compressibility anda high surface stiffness and can impart only a slight amount ofelasticity in the thickness direction of the three-dimensional knittedfabric due to the deformation of the connecting threads 130.Consequently, the three-dimensional knitted fabric 210 of the thirdembodiment of the present invention is structured by two or more regionshaving different degrees of surface stiffness.

[0161]FIG. 21 shows a spring characteristic of a muscle portion of thebuttocks of a human body. However, as will be apparent from this graph,when a pressure within a range of 0.1 to 10 N/mm is applied by acircular compressing plate having a diameter of compressing plate havinga diameter of 98 mm to a muscle portion of the buttocks, the springcharacteristic has a small hysteresis loss, and a relatively highlinearity. As compared to this, in a conventional cushion materialhaving a soft elastic structure in which a soft polyurethane slub foamand a viscous elastic polyurethane foam are laminated to each other,while a part of the load characteristic has a spring constant which issubstantially equivalent to that of the present embodiment, and however,hysteresis loss is substantial and restoring force is insufficient. Inview of the aforementioned facts, when the three-dimensional knittedfabric 210 is stretched between the seat frame, a spring constant issubstantially equivalent to that of a muscle portion of the buttocks ofa seated occupant, and hysteresis loss and linearity are alsosubstantially equivalent to those of the spring characteristic of amuscle portion of the buttocks of a seated occupant. Consequently, amuscle portion of the buttocks of a seated occupant hardly deform whenan occupant is seated on the seat, and the required restoring force canbe reliably obtained.

[0162] When the three-dimensional knitted fabric 210 is stretchedbetween the seat frame, in order for the three-dimensional knittedfabric 210 to perform the aforementioned functions, it is essntial thatload characteristics in a thickness direction before stretching be arelatively low hysteresis loss and relatively high linearity. However,in the three-dimensional knitted fabric 210 of the first embodiment ofthe present invention, arrangement density and thickness of theconnecting threads 130 are entirely uniform (see FIG. 5), andaccordingly, the surface of the three-dimensional knitted fabric 210imparts uniform elasticity. Therefore, the three-dimensional knittedfabric is largely affected by a buckling characteristic of theconnecting threads and has a load characteristic which is non-linear andin which hysteresis loss is considerable. Consequently, in thethree-dimensional knitted fabric of the first embodiment of the presentinvention, for example, spring constant becomes excessively largebecause restoring force is given emphasis in order to adjust thethickness and density of the connecting threads. On the other hand, whenthickness or density of the entire connecting threads is reduceduniformly and the spring constant of the three-dimensional knittedfabric approaches that of a muscle portion of a human body, a hysteresisloss increases and restoring force becomes insufficient.

[0163] In contrast to this, in accordance with the third embodiment ofthe present invention, the respective wale portions 223, formed by theaforementioned strip-shaped fabric portions 221 and the connectingthreads 130 to form a main elastic region, are partially provided in thethree-dimensional knitted fabric. Namely, as compared to a conventionalthree-dimensional knitted fabric having two regions with differentcompressibility (surface stiffness) in which the connecting threads arearranged uniformly on the entire surface by using the same materials andmesh organization, in the three-dimensional knitted fabric of thepresent embodiment, a spring characteristic is soft while the requiredrestoring force is maintained. This is clear from the graph in FIG. 20illustrating load characteristics. As compared to the characteristics ofthe three-dimensional knitted fabric of the first embodiment of thepresent invention (Comparative Example 1 (under the same manufacturingconditions as in Example 4 which will be later described, exceptingcompressibility: 13.2%, and compressive elasticity: 98.1%)), in thethird embodiment as in Example 1, a spring constant becomes smaller,spring characteristics become soft, hysteresis loss is reduced, andlinearity is higher. As a result, it can be appreciated that thethree-dimensional knitted fabric 210 of the third embodiment is moreappropriate as a cushion material (outer cover material) for a seatbecause a spring characteristic is substantially equivalent to acharacteristic of a muscle portion of a human body, and the requiredrestoring force (restoration) is possessed.

[0164] In the three-dimensional knitted fabric 210 of the thirdembodiment of the present invention, such characteristics as describedabove can be obtained by forming the three-dimensional knitted fabric inthe same manner as in a case of forming the projections 160. Namely, itis preferable that compressibility of the wale portions 223 as the mainelastic region is 20 to 90%, compressive elasticity of the wale portions223 is 75 to 100%, and a difference of compressibility between theconnecting threads 130 which are directly under the cylinders 222 amongthe wale portions 223 and a portion of the other ground knit fabric 230is equivalent to or greater than 5%. Further, a thickness of each of thewale portions 223 as the main elastic region (a thickness t betweensurfaces of the pair of the ground knit fabrics 220 and 230 which arearranged via the connecting threads 130) is preferably 5 to 100 mm inorder to satisfy a characteristic of a vehicle seat cushion material. Ifthe thickness is smaller than a range of 5 to 100 mm, it is difficult toobtain excellent cushioning performance. If the thickness exceeds thisrange, stability of the shape of the three-dimensional knitted fabriccannot be secured. Further, even when the thickness is within theaforementioned range, if the thickness of the wale portion 223 exceeds50 mm, due to elasticity of the connecting threads 130, stiffening ofcushioning characteristic and approximation of the value to a rigid bodymust be prevented. When relatively thick wale portions are required, itis preferable to design the wale portions by using the connectingthreads 130 with high elasticity so as to impart characteristics havinga large stroke and a soft cushioning performance.

[0165] Further, by considering convenience of sewing operation, athickness of 5 to 30 mm is most preferable. Moreover, thethree-dimensional knitted fabrics 210 are piled in plurality or can beused by being laminated with another elastic member such as Plumaflexand the like. However, in this case, since a spring characteristic ofanother elastic member is an additional consideration, it is preferablethat a thickness per one three-dimensional knitted fabric 210 (thicknesst of each wale portion 223) is 5 to 30 mm, which is of course at thethinner end of the above-described range of thickness.

[0166] For the same reasons as described above, a ratio of the waleportions 223 when projected on a plane per unit area is preferably 1 to99%/m², and more preferably, 30 to 90%/m² particularly when thethree-dimensional knitted fabric is used as a vehicle seat. In order forthe wale portions 223 as the main elastic region to have a ratio perunit area, a width of each of the strip-shaped fabric portions, and aspacing between the adjacent strip-shaped fabric portions are preferablydetermined as described below:

[0167] When both the number of wale portions in a width of eachstrip-shaped fabric portion and the number of wale portions in a spacingbetween the adjacent strip-shaped fabric portions 221 are respectivelyrepresented by W, it is preferable that W is within a range of thefollowing equation:

W=(0.14·E)/2.54˜(15.24 14·E)/2.54

[0168] wherein “E” represents the number of gauges of a knitting machinefor organizing the three-dimensional knitted fabric, “2.54” is a valuein which 1 inch is expressed by a unit of cm. The present inventorsresearched diligently, resulting in the empirically derived coefficientsof “0.14” and “15.24” which can calculate a desired number of waleportions irrespective of the number of gauges of the knitting machine.

[0169] The ratio of the wale portions 223 as the main elastic region perunit area can be modified in accordance with changes of density or widthof the wale portions 223. For example, in order to control slidabilityin the forward direction of the pelvis of a human body and improve shapeadaptability to changes of posture, it is preferable to increase a widthof one wale portion 223 by a portion corresponding to s lumbar of ahuman body, and to make narrower one wale portion 223 by a portioncorresponding to an ishium of a human body.

[0170] The type and thickness of ground threads for forming the groundknit fabrics 220 and 230 are not particularly limited. However, use ofmultifilament threads or spun threads whose thickness is from 167 to2800 decitex is preferable. If the thickness of multifilament threads isless than 167 decitex, it becomes difficult for the three-dimensionalfabric to secure the necessary lumbar strength and the ground threadseasily cause elastic fatigue. If the thickness exceeds 2800 decitex, amanufacturing operation becomes difficult, and the sensation of touchingthe surface of the fabric also deteriorates. It is possible to usemonofilament threads as ground threads. However, from a viewpoint ofsensation of touch or softness of a fabric surface, as described above,it is preferable to use multifilament threads or spun yarns.

[0171] As described above, it is preferable to use monofilament threadshaving a thickness of 167 to 1100 decitex as the connecting threads 130.

[0172] The same materials as those described above can be used forground threads or for the connecting threads 130.

[0173] As in the third embodiment of the present invention, in order toachieve the above-described characteristics with only the fabricknitting organization, a total thickness of mesh formed by the groundthreads and the connecting threads 130 which form the ground knitfabrics 220 and 230 is preferably 330 decitex or more, and morepreferably 420 to 2800 decitex. Therefore, mesh tightness at a portionwhere the connecting threads 130 are joined is improved, projection ofthe connecting threads 130 when pressed by an occupant is prevented, andthe retention of shape is improved. Accordingly, excellent cushioncharacteristics and body pressure distribution characteristics describedabove can be imparted.

[0174] Needless to say, in order for the three-dimensional knittedfabric to impart the above-described characteristics by adjusting theknitting organization, arrangement forms of knit fabrics, ranges ofvarious values, and materials are not limited to those described in theembodiments of the present invention. The knitting organization can alsobe adjusted by any one element or by combining two elements or more of agroup of elements comprising a connecting thread arrangement density, aconnecting thread thickness, a connecting thread length, a connectingthread material, a ground knit fabric mesh shape, a ground knit fabricmesh size, a ground thread material for structuring the ground knitfabric, and a mesh tightness at the connecting portion of the connectingthread and the ground knit fabric.

[0175] (Fourth Embodiment)

[0176] In relation to FIGS. 13 and 14, a description of a fourthembodiment of the present invention will be made hereinafter. Portionsidentical to the third embodiment of the present invention will bedenoted by the same reference numerals. In the three-dimensional knittedfabric according to the present embodiment, in the same manner as in thesecond embodiment of the present invention, the recesses 150 and theprojections 160 are formed on the fabric (where the strip-shaped fabricportions link to each other) which was manufactured in the same manneras the three-dimensional knitted fabric 210 of the third embodiment ofthe present invention in which the projections 160 form the main elasticregion.

[0177] In the fourth embodiment of the present invention, the recesses150 are formed by making a pair of the ground knit fabrics 220 and 230approach one another, and the ground knit fabrics 220 and 230 aredisposed so as to be separated from one another at a predeterminedspacing in a course direction of the three-dimensional knitted fabric210 of the third embodiment of the present invention. In the presentembodiment, since the recesses 150 are formed among the strip-shapedfabric portions (among which cylinders are formed), the connectingthreads 130 in the recesses 150 are inclined or flexed, and the adjacentconnecting threads 130 are entangled and joined together. As a result,both side portions of the connecting threads 130 which interpose theentangled portions 130 a therebetween act as respectively independentspring elements, in relation to the ground knit fabrics 220 and 230 towhich the connecting threads 130 are joined. Accordingly, asschematically shown in FIG. 15, a structure, which appears to be onespring element having a substantially arch-shaped cross section, isformed in one recess 150 as far as the entangled portion 130 a of theentangled connecting threads 130 to the entangled portion 130 a of theentangled connecting threads 130 in the adjacent recess 150.

[0178] Thus, when compressive deformation of the projections 160 occursdue to a load mass, as compared with the case of the third embodiment ofthe present invention when compressive deformation of the wale portions223, buckling strength of the connecting threads 130 deteriorates,making it difficult for the connecting threads to impart bucklingcharacteristics. As a restoring force, as shown by an imaginary line inFIG. 5, an elastic function in a bending direction of the springelements, which have arch-shaped cross-sections and include theentangled connecting threads 130, becomes relatively larger. As aresult, since the three-dimensional knitted fabric of the fourthembodiment of the present invention is structured in the same manner asin the third embodiment of the present invention except that therecesses 150 and the projections 160 are formed, a spring characteristicof the projections 160 according to the fourth embodiment of the presentinvention becomes smaller such that the recesses 160, which receive avery small load, readily deform at an initial stage, a bucklingcharacteristic becomes insufficient, and accordingly, hysteresis lossbecomes small and linearity high.

[0179] Conversely, when the three-dimensional knitted fabric isstretched across the seat frame, in order to approximate a springcharacteristic of the three-dimensional knitted fabric to that of amuscle portion of a human body, the three-dimensional knitted fabricmust be structured such that the load characteristic of its own has acomparatively high linearity and a relatively small hysteresis loss.Namely, as compared to the third embodiment of the present invention inwhich realization of such characteristics as described above isattempted merely by a knitting organization, the three-dimensionalknitted fabric of the present invention in which the projections 160 areformed can impart the required characteristics even if conditions of theknitting organization of the ground knit fabrics 220 and 230, and thearrangement of the connecting threads 130 are less stringent.

[0180] In this respect, as is apparent from a load characteristic shownin FIG. 20, when the three-dimensional knitted fabric according to athird embodiment of the present invention (Example 1) is compared withthat of the first embodiment of the present invention (ComparativeExample 1), hysteresis loss decreases and linearity becomes higher.However, in the fourth embodiment of the present invention (Example 2),hysteresis loss decreases considerably and linearity becomes muchhigher. Further, since a spring performance in the bending direction ofthe spring elements which have substantially arch-shaped cross sectionsis used, a spring constant is low, and a cushioning structure is therebyconsiderably softer than that in the third embodiment of the presentinvention.

[0181] In the fourth embodiment of the present invention, as describedabove, by entangling the connecting threads 130 in the recesses 150 asdescribed above, elasticity extends and contacts in a directionsubstantially orthogonal to a line along which the recesses 150 are alsoformed. For this reason, when the three-dimensional knitted fabric isstretched over the recesses 150, not only is spring performance impartedin a thickness direction of the three-dimensional knitted fabric and inthe bending direction of the spring elements having substantiallyarch-shaped cross sections, but also elasticity (spring performance)occurring in a plane direction orthogonal to the thickness direction ofthe three-dimensional knitted fabric is additionally imparted to thethree-dimensional knitted fabric, thus contributing to a decrease inspring constant. Since the three-dimensional knitted fabric according tothe fourth embodiment of the present invention has such acharacteristic, as described in the second embodiment of the presentinvention with reference to FIG. 3, it is preferable that the seat isstretched such that projections are dispersed in the widthwise direction(Y direction) of the seat.

[0182] Here, means for forming the recesses 150 will be explained.First, the recesses 150 can be formed at any points. However, therestoring force applied from the recesses 150 in the thickness directionof the three-dimensional knitted fabric is not important. Further, byentangling portions of the connecting threads 130, the recesses 150 arerather used in order to form the projections 160 into the springelements having substantially arch-shaped cross sections. Therefore, theconnecting threads 130 among the recesses 150 do not need higharrangement density. Accordingly, the three-dimensional knitted fabriccan be made compact. Consequently, in the fourth embodiment of thepresent invention in which the third embodiment of the present inventionis used unchanged, a portion of the three-dimensional knitted fabricwhich is included in the cylinders 222 among the strip-shaped fabricportions 221 in the third embodiment of the present invention shown inFIG. 9, together the communicating portion 224 are preferably madethinner in the wale direction of the three-dimensional knitted fabric,such that the connecting threads 130 included in the portion of thethree-dimensional knitted fabric and the communicating portion 224 canbe entangled (crossed).

[0183] As in the first embodiment and a fifth embodiment of the presentinvention (which will be described later), the arrangement densities ofconnecting threads of projections and recesses can be made equivalent.

[0184] The arrangement density of the connecting threads in the recessescan be made higher than in the projections, depending on the thicknessand the knitting organization of the connecting threads. Further, thethree-dimensional knitted fabric can be formed by changing one or two ormore of a group of the elements comprising an arrangement density of theconnecting threads among the recesses 150 and the projections 160, athickness of the connecting threads 130, a length of the connectingthreads 130, and a material of the connecting threads 130, and a meshshape and mesh size of the ground knit fabrics 220 and 230, a materialof ground threads for structuring the ground knit fabrics 220 and 230,and a mesh tightness at the connecting portions of the connectingthreads 130 and the ground knit fabrics 220 and 230. Accordingly,elastic function of the spring elements, which have substantiallyarch-shaped cross-sections, can be appropriately adjusted. Further, aswill be described later, when the ground knit fabrics 220 and 230 aremade to approach one another and compressed, the connecting threads 130in the recesses 150 are made thinner, whereby operations can besimplified.

[0185] As shown in FIG. 10, before the recesses 150 are formed, theconnecting threads 130, which are included in the recesses 150, arecrossed with each other and inclined in relation to each other under thecylinders 222 among the strip-shaped fabric portions 221. Accordingly,the connecting threads 130 are entangled and joined at the crossingportions of the connecting portions 130, whereby it becomes easier tosupport diagonally the side portions of the projections 160, andaccordingly, the spring elements having substantially arch-shaped crosssections can be formed easily.

[0186] Each of the recesses 150 can be formed into an arbitrary shape,and can be formed in an arbitrary direction along the surface of thethree-dimensional knitted fabric. For example, in accordance with thefourth embodiment of the present invention, the recesses 150 are formedin the wale direction while being separated from one another in thecourse direction at a predetermined spacing, so that the projections 160can be arranged in parallel to one another. Further, the recesses 150can be formed in the wale direction so as to be separated from oneanother at a predetermined spacing, whereby, as shown in FIGS. 38A and38B, the projections 160 can be arranged in a lattice form or astaggered form.

[0187] The recesses 150 can be formed from one side of the pair of theground knit fabrics 220 and 230: however, as shown in fourth embodimentof the present invention, they can be formed from both sides of theground knit fabrics 220 and 230. Examples of means for forming therecesses 150 by getting the ground knit fabrics 220 and 230 close to oneanother, include welding means, bonding means, and sewing means by usinga sewing machine, and means in which molten fabrics are interposedbetween the ground knit fabrics 220 and 230 and then molten. Amongthese, use of vibration welding means is preferable because it canprevent the welded portions from forming a rigid body and has highbonding strength.

[0188] The projections 160 as a main elastic region in thethree-dimensional knitted fabric according to the fourth embodiment ofthe present invention preferably have compressibility, compressiveelasticity and thickness which are exactly the same as those of the waleportions 223 as a main elastic region in the third embodiment of thepresent invention. Further, the compressibility difference between theprojections 160 and the recesses 150 of the present embodimentpreferably has the same range, which is equal to or greater than 5%, asthat in the third embodiment of the present invention.

[0189] The ratio of the projections 160 per unit area as a main elasticregion when projected on a plane has the same preferable range as thatof the wale portions 223 of the third embodiment of the presentinvention. Further, it is preferable that the number of wales W perwidth of the projection 160 and spacing between adjacent projections160, and the number of wales W are determined in the same manner asthose in the third embodiment of the present invention, in which thenumber of wales W has a range which is represented by the equation:W=(0.14·E)/2.54˜(15.24 14·E)/2.54. Moreover, as shown in FIG. 14, whenthe recesses 150 are projected on a plane, a substantially flat portionof a root portion is used as a width b, and when the projections 160 areprojected on a plane, a spacing between the substantially flat portionsof the adjacent recesses 150 is a width.

[0190] The preferable type and thickness of ground threads for formingthe ground knit fabrics 220 and 230 and the connecting threads 130 arein the same range as those in the third embodiment of the presentinvention. Substantially the same materials as those in the thirdembodiment of the present invention can be used. However, when therecesses 150 are formed by vibration welding, use of a thermoplasticresin is preferable. Examples of the thermoplastic resin include:thermoplastic polyester resins such as polyethylenetelephthalate (PET)and polybutylencterephthalate (PBT), polyamide resins such as nylon 6and nylon 66, or two or more of these resins can be used in combination.

[0191] However, in the fourth embodiment of the present invention, theconnecting threads 130 are partially entangled and joined so thatprotrusion of the connecting threads can be prevented. Accordingly,tightness of a mesh which is formed by the ground threads forstructuring the ground knit fabrics 220 and 230, and the connectingthreads 130 can be made lower than that in the third embodiment of thepresent invention, and the total thickness of the mesh can be madewithin an even narrower range than this, whereby the ground knit fabrics220, 230 can impart a soft touch.

[0192] (Fifth Embodiment)

[0193]FIG. 17 shows a cross sectional view of a three-dimensionalknitted fabric according to a fifth embodiment of the present invention.The three-dimensional knitted fabric has the recesses 150 and theprojections 160 in the same manner as in the fourth embodiment of thepresent invention, except that both of the ground knit fabrics 330, 340are formed by a flat fabric organization which is continuous both in thewale direction and the course direction, in the same manner as the otherground knit fabric 230 of the third embodiment of the present invention,as shown in FIG. 13. Further, the present embodiment is structured inthe same manner as the previous embodiments except that, before therecesses 150 are formed, the connecting threads 350 are arranged with auniform arrangement density on the entire surface of thethree-dimensional knitted fabric and exclude any rough arrangementportions. With regard to other conditions, the present embodiment isstructured in exactly the same manner as in the fourth embodiment of thepresent invention. Consequently, the fifth embodiment of the presentinvention is structured substantially in the same manner as the secondembodiment of the present invention.

[0194] In the fifth embodiment of the present invention, since theprojections 160 as the main elastic region are partially formed, thesame characteristic as in the fourth embodiment of the present inventioncan be imparted. FIG. 20 shows Example 3 in which a load characteristicof the three-dimensional knitted fabric is structured in the same manneras in the fifth embodiment of the present invention. As is apparent fromthis graph, as compared to a conventional three-dimensional knittedfabric, the three-dimensional knitted fabric in the present embodimenthas lower spring constant, lower hysteresis loss, and higher linearity.Further, in FIG. 20, a load characteristic in Example 3 has a springconstant lower than that in Example 2 which is structured in the samemanner as in the fourth embodiment of the present invention. This isbecause the diameter of each connecting thread used in Example 3 wasnarrower than that of each connecting thread used in Example 2.

[0195] (Sixth Embodiment)

[0196]FIG. 18 shows a cross sectional view of a three-dimensionalknitted fabric according to a sixth embodiment of the present invention.A three-dimensional knitted fabric of the sixth embodiment of thepresent invention has the recesses 150 and the projections 160 in thesame manner as in the fourth and fifth embodiments of the presentinvention. However, as shown in FIG. 19, the first ground knit fabric430 is formed by a rhomboid mesh organization in which portions 420 afor forming the projections 160 are continuous in the wale direction,and by a organization in which portions 410 a for forming the recesses150 are continuous both in the wale direction and in the coursedirection. Further, the other ground knit fabric 440 is structured inthe same manner as the other ground knit fabric 230 in the thirdembodiment of the present invention shown in FIG. 12, and accordingly,is formed by a flat fabric organization which is continuous both in thewale direction and in the course direction. Further, a portion ofconnecting threads 450 on which the recesses 150 are formed has aslightly higher density than a portion of the connecting threads 450 onwhich the projections 160 are formed. With regard to other conditions,the sixth embodiment of the present invention is structured in the samemanner as in the fourth embodiment of the present invention.

[0197] Also in the sixth embodiment of the present invention, since theprojections 160 as the main elastic region are partially formed on thethree-dimensional knitted fabric, the same characteristics as those inthe fourth embodiment of the present invention can be imparted. Namely,as shown in FIG. 20, as compared to a conventional three-dimensionalknitted fabric, the load characteristic of the three-dimensional knittedfabric in the sixth embodiment of the present invention (Example 4) hasa lower spring constant, a smaller hysteresis loss, and a higherlinearity. However, the spring constant of the present embodiment ishigher than those in Examples 1 to 3 of the previous embodiments of thepresent invention because, in the present embodiment, while theconnecting threads having the same diameter as those in Examples 1 and2, and however, the connecting threads were arranged with higherdensity.

[0198] The three-dimensional knitted fabric described above is suitablyused as a cushion material (including outer cover material) by beingstretched across a seat frame for a variety of seats such as a vehicleseat for automobiles or trains, office chair seats, and furniturechairs. However, when the three-dimensional knitted fabric is stretchedacross the seat frame, as described above, it is preferable to stretchthe three-dimensional knitted fabric by an elongation ratio within 5%.In this way, it is easier to form a structure having a springcharacteristic close to a characteristic of a muscle portion of a humanbody as shown in FIG. 21, which will be described later.

[0199] In the second, fourth, fifth and sixth embodiments of the presentinvention, projections are used as the main elastic region, while in thethird embodiment of the present invention, the wale portions are used asprojections, namely, the wale portions linked to each other throughcommunicating portions and operating as a main elastic region. Inconsideration of ease of manufacturing easiness and characteristicsimparted by the three-dimensional knitted fabric when it is used for avehicle seat, it is preferable that the wale portions are structured asdescribed above and operate as the main elastic region. However, bychanging the thickness of connecting threads and ground threads and byadjusting the knitting organization, it is also possible to use recessesas a main elastic region with a high compressive elasticity as long asthe recesses exhibit characteristics which are substantially equivalentto those of the above-described projections.

[0200] In the above description, an example has been explained in whichthe strip-shaped fabric portions are formed by cylinders. However, it ispossible to organize the ground knit fabrics by alternately arranging alarge number of roughly knitted portions extending in a predetermineddirection and a large number of densely knitted portions extending in apredetermined direction. Further, instead of the strip-shaped fabricportions, the densely knitted portions can be used, and instead of thecylinders, the roughly knitted portions can be used.

[0201] An example has been described in which the main elastic region isstructured by the projections or the wale portions. However, shaggyfibers can be implanted on a surface layer portion of thethree-dimensional knitted fabric so as to form a portion having anelastic compliance larger than that of an occupant's pressing a seatcushion.

[0202] (Manufacturing Conditions)

[0203] Specific manufacturing conditions of a three-dimensional knittedfabric which is able to impart the above-described functions will beexemplified hereinafter. Further, the three-dimensional knitted fabricof Manufacturing Example 1 has a structure in which recesses andprojections are not formed, as shown in FIG. 9, which comprises the waleportions (strip-,shaped portions) 223 which are separated from oneanother at a spacing of one wale or plural wale portions and thecylinders 222 among the wale portions 223 so as to connect to oneanother adjacent wale portions. The communication portions 224 areformed in the cylinders 222 at a spacing of one or a few courses. InManufacturing Examples 2 to 4, projections and recesses are formed asshown in FIGS. 13 and 14.

MANUFACTURING EXAMPLE 1

[0204] knitting machine: double-russell (9 gauges/2.54 cm, distancebetween cylinders: 15 mm) wale density: 10 threads/2.54 cm coursedensity: 14 threads/2.54 cm finished thickness (distance betweensurfaces of the pair of the 11.5 mm ground knit fabrics): ground threadsof the first ground knit fabric: 1170 decitex/96f polyester/BCFmultifilament (crimped threads) ground threads of the other ground knitfabric: 660 decitex/192f polyester/BCF multifilament (crimped threads)connecting threads: 660 decitex/1f polyester knitting organization ofthe one ground knit fabric: variation organization of two course meshknitting organization of the other ground knit fabric: queen's cordtotal thickness of a mesh formed by ground threads of the first 1830decitex (a partial thickness: 3000 ground knit fabric and the connectingthreads: decitex) total thickness of a mesh which is formed by groundthreads of the 980 decitex other ground knit fabric and the connectingthreads: compressibility of wale portions: 49.5% compressive elasticityof wale portions: 98.9% compressibility difference between the waleportions and the other  5.2% portions: width of a wale portion: 6 waleswidth of a cell: 1 wales

MANUFACTURING EXAMPLE 2

[0205] knitting machine: double-russell (9 gauges/2.54 cm, distancebetween cylinders wale density: 10 threads/2.54 cm course density: 14threads/2.54 cm finished thickness (a distance between surfaces of thepair of the 11.5 mm ground knit fabrics): ground threads of the firstground knit fabric: 1170 decitex/96f polyester/BCF multifilament(crimped threads) ground threads of the other ground knit fabric: 660decitex/192f polyester/BCF multifilament (crimped threads) connectingthreads: 660 decitex/1f polyester knitting organization of the firstground knit fabric: variation organization of two course mesh knittingorganization of the other ground knit fabric: queen's cord totalthickness of a mesh which is formed by the ground threads of 1880decitex (partial thickness: 3000 the first ground knit fabric and theconnecting threads: decitex) total thickness of a mesh formed by theground threads of the 1980 decitex other ground knit fabric and theconnecting threads: compressibility of projections: 57.9% compressiveelasticity of projections: 98.8% compressibility difference betweenprojections and recesses: 57.8% vibration welding conditions ofrecesses: pressure 18.2 kgf/m², amplitude: 1.0 mm, and time: 1.2 secwidth of a projection: 5 wales width of a recess: 2 wales

MANUFACTURING EXAMPLE 3

[0206] knitting machine: double-russell (9 gauges/2.54 cm, a distancebetween cylinders: 15 mm) wale density: 9.8 threads/2.54 cm coursedensity: 12.8 threads/2.54 cm finished thickness (distance betweensurfaces of the pair of 12.05 mm ground knit fabrics): ground threads ofthe one ground knit fabric: 1170 decitex/384f ground threads of theother ground knit fabric: 560 decitex/1f connecting threads: 560decitex/1f knitting organization of the one ground knit fabric: 1 repeattwo course mesh knitting organization of the other ground knit fabric:queen's cord total thickness of mesh formed by the ground threads of thefirst 1730 decitex ground knit fabric and the connecting threads: totalthickness of mesh formed by the ground threads of the other 1120 decitexground knit fabric and the connecting threads: compressibility ofprojections: 89.1% compressive elasticity of projections:  100%compressibility difference between projections and recesses: 89.0%vibration welding conditions of recesses: pressure 21.7 kgf/m²,amplitude: 1.0 mm, and time: 1.0 sec width of projections: 6 wales widthof recesses: 2 wales

MANUFACTURING EXAMPLE 4

[0207] knitting machine: double-russell (9 gauges/2.54 cm, distancebetween cylinders: 15 mm) wale density: 9 threads/2.54 cm coursedensity: 13.5 threads/2.54 cm finished thickness (distance betweensurfaces of the pair of the 11.5 mm ground knit fabrics): ground threadsof the first ground knit fabric: 1170 decitex/96f ground threads of theother ground knit fabric: 660/decitex/192f connecting threads: 660decitex/1f knitting organization of the one ground knit fabric:projections: 1 repeat 4 course mesh recesses: W atlas deformationknitting organization of the other ground knit fabric: queen's cordtotal thickness of a mesh which is formed by the ground threads 2050decitex (partial thickness: 3220 of the first ground knit fabric and theconnecting threads: decitex) total thickness of a mesh formed by theground threads of the 1540 decitex other ground knit fabric and theconnecting threads: compressibility of projections: 20.0% compressiveelasticity of projections: 94.3% compressibility difference betweenprojections and recesses:  6.8% vibration welding conditions ofrecesses: pressure 18.2 kgf/m², amplitude: 1.0 mm, and time: 1.2 secwidth of projections: 5 wales width of recesses: 3 wales

EXAMPLE 1

[0208] The three-dimensional knitted fabric which was manufactured inManufacturing Example 2 was used as the upper elastic member 31 d forstructuring the cushion material for the seat portion 31. As shown inFIG. 3, the projections 160 were arranged such that the longitudinaldirection of the projections 160 corresponded to the left-rightdirection of the seat, and the elastic compliance thereof was determinedby the flexure amount in relation to the pressure value. Thethree-dimensional knitted fabric for structuring the upper elasticmember 31 d was arranged at an elongation percentage of 0%. As shown inFIGS. 1 and 2, the intermediate elastic member 31 c formed by thethree-dimensional knitted fabric, the mesh structure elastic member 31b, and the metal springs 31 a were disposed under the upper elasticmember 31 d.

[0209] The three-dimensional knitted fabric for forming the intermediateelastic member 31 c was manufactured in the same manner as inManufacturing Example 2 except that recesses and projections were notformed thereon. For the mesh structure elastic member 31 b, Plumaflex(product name) was used, supported by four metal springs at both theright and left sides thereof. Further, the mesh structure elastic member31 b was provided at a distance within a range from 140 mm to 290 mmfrom the seat surface rear end, and was provided at the seat portionwhich the vicinity of a tuber ishiadicum bottom portion of the seatedoccupant contacts and the rearward-direction portion therefrom such thatthe mesh structure elastic member 31 b and the metal springs 31 a hardlyimparted an elastic performance. Further, the metal springs 31 a in thisExample 1 had a diameter of 2.6 mm, a length of 54.6 mm, a mean diameter16.1 mm, and a total of 20 winds, and a spring constant of 0.55 N/mm.

[0210] A circular 98 mm-diameter pressuring plate applied pressure tothe three-dimensional knitted fabric at a speed of 50 mm per minute fromthe surface to a pressure value of 100 N, and measured a flexure amountin relation to a pressure amount, at distances of 150 mm from the seatsurface rear end (the vicinity of a tuber ishiadicum bottom portion), of250 mm from the seat surface rear end, and of 350 mm from the seatsurface rear end (the vicinity of the front edge portion 41 of the seatportion), of the cushion material for the seat portion 31 having theabove-described structure in Example 1. As a means of comparison,polyurethane foam with a thickness of 105 mm at a distance of 150 mmfrom the seat surface rear end (the vicinity of a tuber ishiadicumbottom portion), with a thickness of 75 mm at a distance of 250 mm fromthe seat surface rear end, and with a thickness of 50 mm at a distanceof 350 mm from the seat surface rear end was used as a cushion material.Then, a flexure amount in relation to a pressure amount of this wasdetermined in the same manner as the aforementioned cushion material inExample 1, at distances of 150 mm from the seat surface rear end, 250 mmfrom the seat surface rear end, and 350 mm from the seat surface rearend (the vicinity of the front edge portion 41 of the seat portion). Theresults were shown in FIGS. 23 to 25. Further, the circular 98mm-diameter pressurizing plate applied a pressure to thethree-dimensional knitted fabric from the seat surface rear end of theseat portion at a distances of 150 mm, 250 mm, and 350, respectivelycorresponding to the vicinity of an ishium of a seated occupant, 100 mmdownward from the ishium, and 200 mm downward from the ishium. Pressurewas compressed to 20 W and the results were shown in FIG. 22. Further,the results shown in FIG. 22 have also been incorporated in FIGS. 23 to25.

[0211] As is apparent from FIG. 23, an elastic compliance when areaction force was applied to an extending side of the cushion materialat 150 mm from the seat surface rear end had hysteresis equivalent to orgreater than that of elastic compliance characteristics in Example andComparative Example, and had a fluctuation characteristic tendencysimilar to that of elastic compliance of a human body.

[0212] As shown in FIG. 24, in Example, elastic compliance decreasedwhen linearity became higher and a reaction force was applied to anextending side of the cushion material, on the contrary, in ComparativeExample as shown in FIG. 23, the characteristic did not show anynoticeable change as compared to the fluctuation characteristic at adistance of 150 mm from the seat surface rear end and exhibited a strongtendency of non-linearity.

[0213]FIGS. 26 and 27 show elastic compliance at distances of 150 mm and250 mm from the seat surface rear in Example, and elastic compliance atdistances of 150 mm and 250 mm from the seat surface rear in ComparativeExample, by respectively overlapping characteristics with one another.It can be observed from these graphs that characteristics in Example hadhigh linearity at a distance of 250, and that characteristics inComparative Example had hardly changed. In this way, in Example,linearity is high at the seat portion which the vicinity of a pelvisfront portion of a seated occupant contacts. Therefore, when an occupantis seated on the seat, a dam-like portion is formed at the seat portionwhich the vicinity of a pelvis front portion of a seated occupantcontacts, and the seat portion which the vicinity of a tuber ishiadicumbottom portion of a seated occupant contacts and the rearward-directionportion therefrom relatively sink in the seat. Accordingly, it was notedthat slidablity of buttocks of a seated occupant in a forward directioncan be prevented, and seating stability when an occupant is seated canbe improved.

[0214] As is apparent from FIG. 25, in Example, elastic compliance whena reaction force is applied to an extending side of a front edge portionof the seat portion is greater than elastic compliance of a human body.However, in Comparative Example, the elastic compliance when a reactionforce is applied to an extending side of a front edge portion of theseat portion is substantially equivalent to that of a human body.

[0215] A size of a 98 mm-diameter pressurizing plate substantiallycorresponds to a portion of the seat portion which one of the thighs ofa seated occupant contacts. In Example, as described above, since thefront edge portion of the seat portion has large elastic compliance, itis effective to prevent the impeding of blood flow into the thighs of aseated occupant. Moreover, it was noted that when the thighs are moved,a reaction force applied in the region of the seat portion contacts isnot large and a smooth pedal operation can be facilitated.

EXAMPLE 2

[0216] A human being with a JM96 (load dispersion to the cushion: 85 kg)was seated on the above-described seat. A platform of a pressureapplying apparatus was set at a lower portion of a seat cushion portion.A vibration transmitting ratio (G/G) in relation to a frequency wasmeasured. The results are shown in FIG. 28 by a bold line. As a means ofcomparison, a vibration characteristic of a seat using polyurethane foamis shown by a narrow line.

[0217] If a vibration transmitting ratio (G/G) is excessive, a transientresponse quality deteriorates and because vibration remains, ridingcomfort is affected. However, in this respect, preferably, a seat usingthe three-dimensional knitted fabric imparts a characteristic which islower than that of a seat using polyurethane foam.

[0218] An oscillation at 2 Hz or less which vibrates the very skeletonof a human body will largely influence vehicle riding comfort. However,in the case of the seat according to the present embodiment, oscillationpeaks were at between 2 Hz and 5 Hz, which are lower frequencies thanthose when polyurethane foam was used as a cushion material. Avibration-transmitting ratio in a range of 6 to 8 Hz which oscillateswith the viscera of a seated occupant was relatively small as comparedwith a case where polyurethane foam was used for a cushion material.Consequently, the seat of the present invention is excellent from aviewpoint of vibration absorbing performance.

[0219] As shown in FIG. 29, when a relative vertical vibrationtransmitting characteristic of the cushion material and that of a waistportion of a human body in relation to a vehicle floor were examined, itwas noted that a displacement of the cushion material using thethree-dimensional knitted fabric was in a range of lower frequency andwas relatively larger than that of the cushion material usingpolyurethane foam. Namely, in the cushion material using thethree-dimensional knitted fabric, when a pressure was applied to a widearea of the three-dimensional knitted fabric, the entire connectingthreads flexed. However, when a pressure was applied to a narrow rangeof a dimension of the three-dimensional knitted fabric, a pressure wasapplied to the connecting threads themselves, and the connecting threadswere displaced between the connecting threads and the ground fabrics. Atthis time, a clone frictional force was generated, overcomes elasticityof the connecting threads in a bending direction thereof, and therebycausing a delay in restoration of elasticity. Consequently, a phasedelay to the inputted vibration became larger, and vibration energy canbe absorbed, and a vibration-transmitting ratio could be suppressed to alow level.

What is claimed is:
 1. A seat comprising: a seat frame; and a cushionmaterial supported by the seat frame and having a three-dimensionalknitted fabric which is formed by joining, with connecting threads, apair of ground knit fabrics which are disposed so as to be separatedfrom one another, wherein the cushion material including a first regionwhose elastic compliance when a reaction force is applied to anextending side of the cushion material when an occupant is seated on theseat is substantially equivalent to an elastic compliance of a portionof the occupant's body pressing the cushion material and a second regionwhose elastic compliance is larger than that of the first region.
 2. Theseat of claim 1, wherein, when a load applied to a contracting side ofthe cushion material when the occupant is seated on the seat, and areaction force which is applied to an extending side of the cushionmaterial in response to the load which has been applied to thecontracting side of the cushion material are in equilibrium, an elasticcompliance of the second region when a micro-reaction is applied to anextending side of the cushion material is larger than that of a humanbody portion pressing the cushion material.
 3. The seat of claim 1,wherein the first region and the second region are laminated to oneanother such that the second region is positioned on a top layer portionof a seat portion, or the first region and the second region aredisposed such that the second region is positioned at a front edgeportion of the seat portion, and the first region is positioned at apredetermined region including a tuber ishiadicum of the occupant. 4.The seat of claim 1, wherein a lower portion of the first region has aregion which elastic compliance is smaller than that of the human bodyportion.
 5. A seat comprising: a seat frame; and a cushion materialincluding a three-dimensional knitted fabric supported by the seat frameand formed by joining, with connecting threads, a pair of ground knitfabrics which are disposed so as to be separated from one another,wherein the cushion material includes a first region whose elasticcompliance when a reaction force is applied to an extending side of thecushion material when an occupant is seated on the seat is substantiallyequivalent to an elastic compliance of a portion of the occupant's bodypressing the cushion material and which first region is positioned at apredetermined region including a seat portion which a tuber ishiadicumbottom portion of the seated occupant contacts, a second region whoseelastic compliance is larger than the elastic compliance of the firstregion and which is positioned in the vicinity of a front edge portionof the seat portion, and a third region whose elastic compliance issmaller than the elastic compliance of the first region and which ispositioned at a position corresponding to a vicinity of a pelvis frontportion of the seat portion the seated occupant contacts.
 6. The seat ofclaim 1, wherein the cushion material is structured such that thethree-dimensional knitted fabric is stretched across the seat frame, anda portion of the stretched three-dimensional knitted fabric is mountedon an elastic member whose size is smaller than the three-dimensionalknitted fabric and whose elastic compliance characteristic issubstantially linear, and the cushion material comprises the firstregion in which the elastic member exists beneath the three-dimensionalknitted fabric and the second region in which no elastic member existsbeneath the three-dimensional knitted fabric.
 7. The seat of claim 6,wherein the elastic member is provided at a region which has apredetermined region including a seat portion which a tuber ishiadicumbottom portion of the seated occupant contacts, and which excludes avicinity of a front edge portion of the seat portion and arearward-direction portion from the predetermined region.
 8. The seat ofclaim 6, wherein a region, whose elastic compliance when a reactionforce is applied to an extending side of the cushion material when theoccupant is seated on the seat is smaller than an elastic compliance ofa human body portion pressing the cushion material and whose linearityof displacement is higher than that of a predetermined region includinga seat portion which a tuber ishiadicum bottom portion of the seatedoccupant contacts, is provided at the seat portion which the vicinity ofthe pelvis front portion of the seated occupant contacts, between thepredetermined region including a seat position which a tuber ishiadicumbottom portion of the seated occupant contacts and a front edge portionof the seat portion.
 9. The seat of claim 6, wherein thethree-dimensional knitted fabric is stretched across the seat frame suchthat a portion from the seat surface rear end to a predetermined regionincluding a tuber ishiadicum bottom portion of the seated occupantcontacts is slackened to a predetermined amount, while a correspondingseat position corresponding to a vicinity of a pelvis front portion ofthe seated occupant, between the predetermined region including the seatportion which a tuber ishiadicum bottom portion of the seated occupantcontacts, and a front edge portion of the seat portion is slackened to asmaller amount than predetermined amount.
 10. The seat of claim 6,wherein the three-dimensional knitted fabric is stretched across theseat frame such that a portion from a seat surface rear end to apredetermined region including a tuber ishiadicum bottom portion isslackened by providing 5 to 60 mm of extra width in relation to theentire width of the seat frame for structuring the seat frame and aposition corresponding to a vicinity of a pelvis front portion betweenthe predetermined region including a tuber ishiadicum bottom portion anda front edge portion of the seat portion is slackened by providing 0 to20 mm of extra width.
 11. The seat of claim 6, wherein the elasticmember comprises a mesh-structure elastic member, a sheet-structureelastic member, or a mesh or sheet-structure elastic member which issupported by a metal spring, wherein the elastic member imparts largeelasticity to a position corresponding to a vicinity of a pelvis frontportion of the seated occupant.
 12. The seat of claim 1, wherein thethree-dimensional knitted fabric further comprises a portion which has ahigh surface stiffness, and a main elastic region which has a lowsurface stiffness and imparts a major restoring force in relation tocompressive deformation.
 13. The seat of claim 12, wherein thethree-dimensional knitted fabric comprises at least two portions eachhaving different compressibility, the portions having the highestcompressibility being structured as a main elastic region which impartsa major restoring force in relation to compressive deformation.
 14. Theseat of claim 13, wherein the main elastic region of thethree-dimensional knitted fabric has compressibility in a range from 20%to 90%, and compressive elasticity in a range from 75% to 100%, andcompressibility difference between the main elastic region and thenon-main elastic region is at least 5%.
 15. The seat of claim 12,wherein recesses and projections are formed on at least one of thesurfaces of the three-dimensional knitted fabric and at least one of therecesses and the projections structures the main elastic region.
 16. Theseat of claim 15, wherein the projections structure the main elasticregion and form substantially arch-shaped cross sections with adjacentrecesses to form a structure which can use elasticity which is appliedin a bending direction of the projections having substantiallyarch-shaped cross sections.
 17. The seat of claim 15, wherein thethree-dimensional knitted fabric is stretched across the seat frame suchthat the projections are formed in a wale form in an arbitrary directionof a surface of the three-dimensional knitted fabric, and theprojections run in a longitudinal direction which corresponds to atransverse direction of the seat at one of a seat portion or both at theseat portion and a back portion.
 18. The seat of claim 15, wherein thethree-dimensional knitted fabric is stretched across the seat frame suchthat the projections of the three-dimensional knitted fabric arearranged in a lattice form or a staggered form, and a direction in whicharrangement density of the main elastic region is high, corresponds to atransverse direction of the seat, at one of a seat portion or both atthe seat portion and a back portion.
 19. The seat of claim 1, whereinthe three-dimensional knitted fabric is stretched across the seat frameat an elongation percentage of less than 5%.
 20. The seat of claim 12,wherein a thickness of the main elastic region of the three-dimensionalknitted fabric ranges from 5 mm to 80 mm.
 21. The seat of claim 12,wherein a percentage per unit area of the main elastic region of thethree-dimensional knitted fabric when projected on a plane is in a rangefrom 30% to 90%/m².
 22. The seat of claim 12, wherein the main elasticregion of the three-dimensional knitted fabric is formed by adjusting aknitted organization.
 23. The seat of claim 22, wherein the knittingorganization of the three-dimensional knitted fabric is adjusted withany one element or by an arbitrarily combination of two elements or moreof a group of elements comprising a connecting thread arrangementdensity, a connecting thread thickness, a connecting thread length, aconnecting thread material, a ground knit fabric mesh shape, a groundknit fabric mesh size a ground thread material for structuring theground knit fabric, and a mesh tightness at the connecting portion ofthe connecting thread and the ground knit fabric.
 24. The seat of claim15, wherein the recesses are formed by joining connecting threadsbetween the pair of ground knit fabrics in a state in which the groundknit fabrics are made to approach one another, and the projectionsstructure the main elastic region.
 25. The seat of claim 15, wherein therecesses of the three-dimensional knitted fabric are formed by one ofwelding, adhesion, stitching, welding using molten fabric, and vibrationwelding.
 26. The seat of claim 15, wherein the three-dimensional knittedfabric is formed so that one element or an arbitrary two or more of agroup of the elements comprising: connecting thread arrangement density,connecting thread thickness, connecting thread length, connecting threadmaterial, ground knit fabric mesh shape, ground knit fabric mesh size aground thread material for structuring the ground knit fabric, and meshtightness at the connecting portion of connecting threads and a groundknit fabric are different in a region of the projections and a region ofthe recesses.
 27. The seat of claim 15, wherein the three-dimensionalknitted fabric is formed such that connecting threads in the region ofthe recesses have an arrangement density which is lower than that ofconnecting threads in the region of the projections for structuring themain elastic region.
 28. The seat of claim 1, wherein the pair of groundknit fabrics, which are disposed so as to be separated from one another,comprise: a first ground knit fabric which is formed by a flat fabricorganization, and a second ground knit fabric which comprises aplurality of strip-shaped knit fabric portions which are arranged so asto extend in a predetermined direction at a predetermined spacing,wherein the three-dimensional knitted fabric is formed by connecting,with connecting threads, the plurality of the strip-shaped knit fabricportions, respectively, to the first ground knit fabric at a region ofthe first ground knit fabric which faces the respective strip-shapedfabric portions, at a region of the first ground knit fabric which facesthe respective cylinders among the respective strip-shaped fabricportions, and at a region of the first ground knit fabric which facesother respective adjacent strip-shaped fabric portions.
 29. The seat ofclaim 28, wherein a hollow portion where connecting threads do not existis formed at a widthwise-intermediate portion of a region where thefirst ground knit fabric faces the strip-shaped knit fabric portions.30. The seat of claim 28, further comprising a plurality ofcommunicating portions where the respective adjacent strip-shaped knitfabric portions link with each other at a plurality of portions whichare separated from one another at a predetermined spacing in anextending direction of the strip-shaped knit fabric portions.
 31. Theseat of claim 28, wherein respective edge portions of the strip-shapedknit fabric portions and the first ground knit fabric are made toapproach one another so that the respective strip-shaped knit fabricportions form projections.
 32. The seat of claim 5, wherein the cushionmaterial vibrates, an elastic compliance of the third region of the seatportion is substantially equivalent to an elastic compliance of a humanbody portion pressing the cushion material.
 33. The seat of claim 8,wherein, when a weight of the seated occupant and a reaction force ofthe cushion material are in equilibrium, and the cushion materialvibrates due to an external pressure, an elastic compliance of the seatposition which corresponds to the vicinity of the pelvis front portionof the seated occupant is substantially equivalent to an elasticcompliance of a portion of the occupant's body pressing the cushionmaterial.
 34. The seat of claim 9, wherein, when a weight of the seatedoccupant and a reaction force of the cushion material are inequilibrium, and the cushion material vibrates due to an externalpressure, the three-dimensional knitted fabric is stretched such that anelastic compliance of the position which corresponds to the vicinity ofthe pelvis front portion of the seated occupant is substantiallyequivalent to an elastic compliance of a portion of the occupant's bodypressing the cushion material.
 35. The seat of claim 10, wherein, when aweight of the seated occupant and a reaction force of the cushionmaterial are in equilibrium, and the cushion material vibrates due to anexternal pressure, the three-dimensional knitted fabric is stretchedsuch that an elastic compliance of the position which corresponds to thevicinity of the pelvis front portion of the seated occupant issubstantially equivalent to an elastic compliance of a portion of theoccupant's body pressing the cushion material.
 36. The seat of claim 11,wherein, when a weight of the seated occupant and a reaction force ofthe cushion material are in equilibrium, and the cushion materialvibrates due to an external pressure, the three-dimensional knittedfabric is stretched such that an elastic compliance of the positionwhich corresponds to the vicinity of the pelvis front portion of theseated occupant is substantially equivalent to an elastic compliance ofa portion of the occupant's body pressing the cushion material.